Anode slurry composition, lithium secondary battery anode including same, and lithium secondary battery

Abstract

The present specification relates to an anode slurry composition for alleviating electrode thermal wrinkling. The composition comprises: an anode active material; a conductive material; and two or more types of cellulose-based binder, wherein the cellulose-based binder comprises carboxymethyl cellulose (CMC) and cellulose nanofibrils (CNF), and the weight ratio (CNF / CMC) of cellulose nanofibrils (CNF) to carboxymethylcellulose (CMC) in the cellulose-based binder is in the range of approximately 0.05 to 3.00.

Description

Negative electrode slurry composition, negative electrode for lithium secondary battery and lithium secondary battery comprising the same

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

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0111309, filed August 24, 2023, and Korean Patent Application No. 10-2024-0113026, filed August 22, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present specification discloses a negative electrode slurry composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery.

[0004] Secondary batteries are attracting attention as power sources for not only small electronic devices such as portable computers, mobile phones, and cameras, but also large electronic devices such as electric vehicles and power storage devices.

[0005] To manufacture these secondary batteries, for example, cylindrical, square, and pouch-shaped batteries are manufactured, and the manufactured batteries are assembled to manufacture, for example, battery packs, which are then used in electric vehicles or power storage devices.

[0006] Meanwhile, in the process of manufacturing a battery, the negative and positive electrodes are manufactured and a separator is interposed to manufacture an electrode assembly, and various studies are being conducted in relation to the process of manufacturing these negative electrodes, positive electrodes, and separators.

[0007]

[0008] This is a process defect phenomenon that occurs during the drying process after electrode coating. The problem is that the electrode temperature at the end of drying rises by the temperature of the drying furnace, causing the foil to thermally expand, but the electrode cannot withstand this and cracks occur.

[0009] A negative electrode slurry composition according to one embodiment of the present invention includes a negative electrode active material, a conductive material, and two or more types of cellulose-based binders, wherein the cellulose-based binders include carboxymethylcellulose (CMC) and cellulose nanofibrils (CNF), and a weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethylcellulose (CMC) in the cellulose-based binder (CNF / CMC) is in a range of about 0.05 to 3.00.

[0010] The fiber width of the above cellulose nanofibrils (CNF) is about 1 nm to 100 nm, and the fiber length is about 10 nm to 5,000 nm.

[0011] The weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethyl cellulose (CMC) in the above binder (CNF / CMC) is in the range of about 0.25 to 0.75.

[0012] The above cellulose-based binder is included in an amount of about 0.5 to 1.5 wt% based on the total weight of the negative electrode slurry composition.

[0013] The above cellulose-based binder is included in an amount of about 0.7 to 1.2 wt% based on the total weight of the negative electrode slurry composition.

[0014] The above carboxymethyl cellulose (CMC) is included in an amount of about 0.4 to 1.5 wt% based on the total weight of the composition.

[0015] The composition further comprises at least one non-cellulosic binder selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinylacetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, and mixtures thereof.

[0016] The above negative active material includes a carbon-based material, a silicon-based material, or a Si-C composite.

[0017] The above conductive material includes at least one selected from the group consisting of graphite, carbon black, carbon-based materials, conductive fibers, fluorinated carbon, metal powder, conductive oxides, and conductive polymers.

[0018] According to another embodiment of the present invention, a negative electrode for a lithium secondary battery comprises: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector; wherein the negative electrode active material layer is formed from the negative electrode slurry composition, and the cellulose nanofibrils (CNF) suppress the occurrence of thermal wrinkles in the negative electrode current collector.

[0019] The negative electrode active material layer of the above negative electrode for the lithium secondary battery has a multilayer structure including an upper active material layer and a lower active material layer, and the upper active material layer and the lower active material layer are formed of negative electrode slurry compositions having different compositions.

[0020] The weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethyl cellulose (CMC) (CNF / CMC) is in the range of about 0.05 to 3.0.

[0021] The weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethyl cellulose (CMC) (CNF / CMC) is in the range of about 0.25 to 0.75.

[0022] The above negative electrode current collector has a thickness of about 2 μm to 10 μm.

[0023] According to another embodiment of the present invention, a lithium secondary battery includes a positive electrode; a negative electrode; and an electrolyte including a lithium salt and a non-aqueous organic solvent, and includes the negative electrode for a secondary battery as the negative electrode.

[0024] The cathode slurry composition according to an embodiment of the present invention can minimize the thermal wrinkling phenomenon that occurs during the drying process after electrode coating in the manufacturing process of an electrode having a relatively thin foil thickness as a current collector. Accordingly, not only can the productivity of the electrode be improved during the manufacturing process, but the energy density of the manufactured battery can also be increased.

[0025] Hereinafter, an electrolyte composition for a lithium metal battery according to an embodiment of the present invention will be described.

[0026] 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.

[0027] 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.

[0028] In this specification, it should be understood that the terms “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.

[0029] As used herein, the terms “about,” “approximately,” and “substantially” are used to mean a range of or near that number or degree, taking into account inherent manufacturing and material tolerances.

[0030] In this specification, “thermal wrinkle occurrence temperature” means the temperature of the drying furnace at which thermal wrinkle occurrence occurs.

[0031] Among the battery manufacturing processes, the electrode manufacturing process includes a process of coating electrode material on a current collector and then drying it. During the electrode drying process, for example, in a drying furnace, the current collector in the form of a foil, which is a substrate that supports the electrode, may wrinkle and crack the electrode. This is called heat wrinkle. This is a process defect that occurs during the drying process after coating the electrode on the current collector, and it mainly occurs in the negative electrode. The cause of heat wrinkle is the difference in the thermal expansion index between the electrode and the foil. At the end of drying, the electrode temperature rises by the temperature of the drying furnace, causing the current collector foil to thermally expand, while the electrode cannot withstand this and cracks occur.

[0032] This thermal wrinkling phenomenon tends to become more severe as the drying temperature increases and the foil thickness decreases.

[0033] Meanwhile, the battery industry has recently been developing in the direction of increasing drying speed and drying temperature to improve electrode productivity and decreasing foil thickness to increase battery energy density, which increases the possibility of thermal wrinkles occurring during the manufacturing process.

[0034] The present invention provides a negative electrode slurry composition capable of minimizing the occurrence of thermal wrinkles in an electrode even in such a harsh environment, and a negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

[0035]

[0036] Cathode slurry composition

[0037] According to one embodiment of the present invention, a negative electrode slurry composition is provided, which includes a negative electrode active material, a conductive material, and two or more kinds of cellulose-based binders, wherein the cellulose-based binders include carboxymethylcellulose (CMC) and cellulose nanofibrils (CNF), and wherein a weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethylcellulose (CMC) in the cellulose-based binder (CNF / CMC) is in a range of about 0.05 to 3.00.

[0038] This negative electrode slurry composition may particularly include cellulose nanofibrils (CNF) as a cellulose-based binder, thereby suppressing thermal wrinkling in the negative electrode current collector. In addition, the level of thermal wrinkling may be improved by applying carboxymethylcellulose (CMC) and cellulose nanofibrils (CNF) as the cellulose-based binder at a specific weight ratio. According to one embodiment, the fiber width of the cellulose nanofibrils (CNF) is about 1 nm to 100 nm, for example, about 3 nm to 10 nm. In addition, the fiber length of the cellulose nanofibrils (CNF) is about 110 nm to 5,000 nm, for example, about 100 nm to 2,000 nm. Meanwhile, the fiber width and length of these cellulose nanofibrils (CNF) can be measured using AFM, SEM, and TEM.

[0039] For example, the weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethylcellulose (CMC) in the cellulose-based binder (CNF / CMC) may range from about 0.05 to 3.00 or from about 0.1 to 1.0. In one embodiment, the weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethylcellulose (CMC) (CNF / CMC) may range from about 0.25 to 0.75. When the above weight ratio range is satisfied, the level of thermal wrinkling can be improved, thereby providing an advantage in electrode production yield.

[0040] In an exemplary embodiment, the cellulose-based binder may be included in an amount of about 0.5 wt% to 1.5 wt% based on the total weight of the negative electrode slurry composition. For example, the cellulose-based binder may be included in an amount of about 0.7 wt% to 1.2 wt% based on the total weight of the negative electrode slurry composition. When the cellulose-based binder content range described above is present, the level of thermal wrinkle occurrence can be significantly improved.

[0041] In an exemplary embodiment, the carboxymethyl cellulose (CMC) may be included in an amount of about 0.4 wt% to 1.5 wt% based on the total weight of the composition. For example, if the carboxymethyl cellulose content is less than about 0.4 wt%, it may be difficult to secure electrode slurry dispersibility due to the low CMC ratio, thereby failing to secure processability.

[0042] Meanwhile, the CNF content relative to the total weight of the composition may be about 0.4 wt% or less. In particular, if the CNF content is higher than necessary, the slurry viscosity may increase, causing a coating process defect and being disadvantageous for uniform electrode production.

[0043] In an exemplary embodiment, the composition may further comprise, in addition to two or more types of cellulosic binders, a non-cellulosic binder. The above non-cellulose binder is a component that assists in the bonding of the negative electrode active material and the conductive material and the bonding to the current collector, and for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinylacetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, and mixtures thereof. However, it is not necessarily limited to this.

[0044] The above non-cellulose binder may be used in an amount of about 1 to 50 parts by weight, or about 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the negative electrode. As a result, the adhesive strength between the negative electrode active material and the current collector and the capacity characteristics of the secondary battery can be maintained relatively well.

[0045] In an exemplary embodiment, the negative electrode active material may include a carbonaceous material, a silicon-based material, or a Si-C composite. For example, a compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. According to one embodiment, the negative electrode active material may include a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; a metallic compound capable of alloying with lithium such as Si, Al, Sn, Pb, Sb, Zn, Bi, In, Mg, Ga, Cd, a Si alloy, a Sn alloy, or an Al alloy; a metallic oxide capable of doping and dedoping lithium such as SiOβ (0 < β < 2), SnO2, vanadium oxide, or lithium vanadium oxide; or a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material.

[0046] In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0047] In an exemplary embodiment, the conductive material may include at least one selected from the group consisting of graphite, carbon black, carbon-based materials, conductive fibers, fluorocarbon, metal powder, conductive oxides, and conductive polymers.

[0048] For example, the conductive material included in the negative electrode is not particularly limited as long as it does not cause side reactions in the internal environment of the lithium secondary battery, does not cause chemical changes in the battery, and has excellent electrical conductivity. According to one embodiment, graphite or conductive carbon can be used. For example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, etc.; carbon-based materials having a crystal structure of graphene or graphite; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powder such as aluminum powder or nickel powder; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives; may be used alone or in combination of two or more, but is not necessarily limited thereto.

[0049] The above-mentioned conductive material may be used in an amount of about 0.5 to 50 parts by weight, or about 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the negative electrode. As a result, the electrochemical properties, such as conductivity and capacity, of the negative electrode and lithium secondary battery can be maintained excellently.

[0050]

[0051] Cathode for lithium secondary battery and lithium secondary battery

[0052] According to another embodiment of the present invention, a negative electrode for a lithium secondary battery is provided, comprising: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector; wherein the negative electrode active material layer is formed of the above-described negative electrode slurry composition, and the cellulose nanofibrils (CNF) suppress the occurrence of thermal wrinkles in the negative electrode current collector.

[0053] In an exemplary embodiment, the negative electrode can be manufactured according to a conventional method known in the art. For example, a negative electrode active material, a conductive material, a binder, and, if necessary, a filler, etc., may be dispersed and mixed in a dispersion medium (solvent) to make a slurry, which may then be applied onto a negative electrode current collector, followed by drying and rolling to manufacture the negative electrode. For example, the slurry may be applied onto a negative electrode current collector using a single layer die coating (SLD) method.

[0054] In an exemplary embodiment, the negative electrode active material layer has a multilayer structure including an upper active material layer and a lower active material layer, and the upper active material layer and the lower active material layer may be formed of negative electrode slurry compositions having different compositions. For example, at least one of the upper or lower active material layers may be formed of the negative electrode slurry composition. Such a multilayer structure may be manufactured by coating and drying using a double layer die coating (DLD) method in a wet on wet manner. On the other hand, when the negative electrode active material layer has a single layer structure, it may be manufactured by coating and drying using a single layer die coating (SLD) method.

[0055] In an exemplary embodiment, the weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethylcellulose (CMC) (CNF / CMC) may be in the range of about 0.05 to 3.0. For example, the weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethylcellulose (CMC) (CNF / CMC) may be in the range of about 0.25 to 0.75. When the weight ratio range is satisfied, the level of thermal wrinkling can be improved, thereby providing an advantage in electrode production yield.

[0056] In an exemplary embodiment, the negative electrode current collector may be, but is not limited to, platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), copper (Cu), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO2), FTO (F doped SnO2), and alloys thereof, as well as copper (Cu) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The negative electrode current collector may have a form such as a foil, a film, a sheet, a punched form, a porous body, or a foam.

[0057] In an exemplary embodiment, the negative electrode current collector may have a thickness of about 2 μm to 10 μm. For example, the negative electrode current collector may have a thickness of about 4 μm to 8 μm. While applying a thin current collector to increase the energy density of the battery, by introducing the negative electrode slurry composition according to an embodiment of the present invention, the possibility of thermal wrinkles occurring during the manufacturing process can be significantly reduced.

[0058] According to another embodiment of the present invention, a lithium secondary battery is provided, which includes a positive electrode; a negative electrode; and an electrolyte including a lithium salt and a non-aqueous organic solvent, and includes the aforementioned negative electrode for a secondary battery as the negative electrode.

[0059] In an exemplary embodiment, the above-described positive electrode can be manufactured by, for example, dispersing and mixing the positive electrode active material, binder, and conductive agent in a dispersion medium (solvent) to make a slurry, applying the slurry on a positive electrode current collector, and then drying and rolling. At this time, the dispersion medium may be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto.

[0060] In addition, the positive electrode current collector may be formed of, but is not limited to, platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO2), FTO (F doped SnO2), and alloys thereof, as well as aluminum (Al) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The positive electrode current collector may be formed in the form of a foil, a film, a sheet, a punched body, a porous body, a foam, or the like.

[0061] Meanwhile, in the lithium secondary battery of the other embodiment, the positive electrode active material is not particularly limited as long as it is a material capable of reversible insertion and de-insertion of lithium ions, and may include, for example, 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.

[0062] According to one embodiment, 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 b D2 (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); Li a 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 dO2 (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).

[0063] 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.

[0064] In addition, the positive electrode may further include a binder and a conductive material in addition to the positive electrode active material described above. Furthermore, the binder and conductive material may be the same as those described above for the negative electrode, and therefore, further description thereof will be omitted.

[0065] Additionally, a filler may be optionally added to the positive electrode as a component that suppresses its expansion. Such filler is not particularly limited as long as it can suppress the expansion of the electrode without causing chemical changes in the battery. Examples of fillers that can be used include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0066] The lithium secondary battery of another embodiment described above may include an electrolyte comprising a lithium salt and a non-aqueous organic solvent. This electrolyte acts as a transport medium for lithium ions between the positive and negative electrodes. These lithium ions exist in the electrolyte in a solvated state, while at the interface between the electrolyte and the electrode, they can be desolvated and inserted into the electrode active material.

[0067] The lithium salt included in the above electrolyte is used as a medium for transferring ions within a lithium secondary battery. The lithium salt is, for example, Li as a cation. + Including, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 -, SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - It may include an anion selected from the group consisting of .

[0068] In one embodiment, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (lithium bis(fluorosulfonyl) imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl) imide, LiN(SO2CF2CF3)2) and LiTFSI (lithium bis(trifluoromethanesulfonyl) imide, LiN(SO2CF3)2).

[0069] The concentration of the above lithium salt can be appropriately changed within a commonly usable range, and can be included in the electrolyte at a concentration of about 0.5 M to 6 M, or a concentration of about 1 M to 5 M.

[0070] In one embodiment, the electrolyte may contain a relatively low concentration of lithium salt, from about 0.5 M to about 2 M, or from about 0.7 M to about 1.5 M. Even in such cases, the lithium secondary battery of another embodiment may exhibit improved output characteristics as the desolvation of lithium ions is accelerated by the action of the electrode of the above-described embodiment.

[0071] Meanwhile, in another embodiment of the invention, the electrolyte may contain a lithium salt at a high concentration of about 2 M to 6 M, or about 2.5 M to 5.5 M. In such a case, the inclusion of a high-concentration lithium salt and the application of the electrode of one embodiment can further accelerate the desolvation of lithium ions, and the output characteristics of the secondary battery can be further improved.

[0072] Meanwhile, the type of non-aqueous organic solvent that can be included in the electrolyte is not particularly limited, and any organic solvent previously known to be applicable to electrolytes of lithium ion batteries, etc., can be used. Examples of such organic solvents include at least one selected from the group consisting of carbonate solvents, ether solvents, nitrile solvents, phosphate solvents, and sulfone solvents.

[0073] In one embodiment, the carbonate solvent may be dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, or methyl (2,2,2-trifluoroethyl) carbonate, and the phosphate solvent may be trimethyl phosphate, triethyl phosphate, or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide.

[0074] In addition, as the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxy ethane, or tetrahydrofuran derivatives such as 2-methyl tetrahydrofuran can be used, and as the nitrile solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile can be used. In addition, as the sulfone solvent, dimethyl sulfone, ethylmethyl sulfone, or sulforane can be used.

[0075] Meanwhile, the electrolyte may further include, in addition to the lithium salt and the non-aqueous organic solvent described above, a diluent that exhibits a solubility in the lithium salt that is at least 10 times lower than that in the non-aqueous organic solvent. The diluent may be an organic solvent that is miscible with the non-aqueous organic solvent while exhibiting substantially no solubility in the lithium salt, for example, an ether solvent having a fluorine-substituted alkyl group, and may include, for example, at least one selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), methoxynonafluorobutane (MOFB), and ethoxynonafluorobutane (EOFB).

[0076] When such a diluent is further included, a high-concentration lithium salt may be locally present in the non-aqueous organic solvent within the electrolyte, and substantially no lithium salt may be present within the diluent. In this way, since a high-concentration lithium salt is locally present in a solvated form within the electrolyte, the output characteristics of the lithium secondary battery can be further improved, while the increase in viscosity and decrease in fluidity of the electrolyte can be reduced. In addition, when the electrode of one embodiment is applied together with such a high-concentration salt electrolyte, lithium ion conductivity can be improved and resistance can be reduced even at low temperatures, thereby reducing the deterioration of low-temperature output characteristics due to high-concentration lithium salt, etc.

[0077] The amount of the diluent used can be adjusted depending on the type of non-aqueous organic solvent and lithium salt, or the overall concentration of the lithium salt, and for example, the diluent: non-aqueous organic solvent can be included in the electrolyte in a molar ratio of about 1:0.2 to 1:5, or about 1:0.5 to 1:2.

[0078] Meanwhile, the lithium secondary battery of another embodiment described above may further include a porous separator interposed between the positive electrode and the negative electrode.

[0079] These porous membranes can be made of olefin polymers such as polyethylene and polypropylene, glass fibers, etc. in the form of sheets, multi-membranes, microporous films, woven fabrics, and non-woven fabrics, but are not necessarily limited thereto. However, porous polyethylene or porous glass fiber non-woven fabric (glass filter) can be used as the membrane, and porous glass filter (glass fiber non-woven fabric) can also be used as the membrane. The membrane can be an insulating thin film having high ion permeability and mechanical strength, and the pore diameter of the membrane can generally be about 0.01 ㎛ to 10 ㎛, and the thickness can generally be about 5 ㎛ to 300 ㎛, but is not limited thereto.

[0080] In addition, in another example of the lithium secondary battery, the separator may not be interposed, and the electrolyte described above may be interposed between the positive and negative electrodes in the form of an electrolyte membrane or electrolyte film. In this case, the electrolyte membrane or electrolyte film may be in the form of a polymer matrix containing the lithium salt and a non-aqueous organic solvent described above, and a well-known polymer-based solid electrolyte or the like may be used as the polymer matrix. In this case, the lithium secondary battery of the other embodiment may be a semi-solid battery that uses a liquid electrolyte and a solid electrolyte in combination.

[0081] Meanwhile, the lithium secondary battery of the above-described other embodiment can be manufactured according to a conventional method in the art. For example, the electrode assembly including the positive electrode, negative electrode, and separator (or electrolyte membrane) can be manufactured by housing it in a case and injecting and impregnating the electrolyte described above.

[0082] These lithium secondary batteries can be applied to battery cells used as power sources for small devices, and are particularly suitable for use as unit cells in battery modules that serve as power sources for medium- to large-sized devices.

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

[0084]

[0085] Comparative Example 1: Cathode with application of CMC-only composition slurry

[0086] The electrode was manufactured by coating the cathode slurry on a 6 μm thick Cu foil using wet-on-wet double layer die coating (DLD) and drying. The upper and lower layers each had a loading of 130 ± 20 mg / 25 cm. 2 Coated with 260±20mg / 25cm 2 This was coated on Cu foil. The slurry compositions of the upper and lower layers are as follows. At this time, the CMC content is 1.15 wt% for both the upper and lower layers.

[0087] - Upper layer composition: graphite / conductive material (carbon black) / CMC / SBR = 97.45 / 0.5 / 1.15 / 0.9

[0088] - Lower layer composition: graphite / conductive material (carbon black) / CMC / SBR = 95.35 / 0.5 / 1.15 / 3.0

[0089]

[0090] Example 1: Cathode with application of slurry with a composition of CNF / CMC=0.25

[0091] A cathode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower layer slurries had the following compositions. The total amount of CMC and CNF in the slurry of each layer was 1.0 wt% (CMC 0.8 wt%, CNF 0.2 wt%), and the weight ratio of CNF to CMC was 0.25.

[0092] - Upper layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 97.6 / 0.5 / 0.8 / 0.2 / 0.9

[0093] - Lower layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 95.35 / 0.5 / 0.8 / 0.2 / 3.0

[0094]

[0095] Example 2: Cathode with application of slurry with a composition of CNF / CMC=0.75

[0096] A cathode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower layer slurries had the following compositions. The slurry composition was changed from Example 1. The total amount of CMC and CNF in the slurry of one layer was 0.7 wt% (CMC 0.4 wt%, CNF 0.3 wt%), and the weight ratio of CNF to CMC was 0.75.

[0097] - Upper layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 97.9 / 0.5 / 0.4 / 0.3 / 0.9

[0098] - Lower layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 95.5 / 0.5 / 0.4 / 0.3 / 3.0

[0099]

[0100] Comparative Example 2: Cathode with application of slurry with a composition of CNF / CMC=0.045

[0101] A cathode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower layer slurries had the following compositions. The total amount of CMC and CNF in the slurry of each layer was 1.15 wt% (CMC 1.10 wt%, CNF 0.05 wt%), and the weight ratio of CNF to CMC was 0.045.

[0102] -Upper layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 97.45 / 0.5 / 1.10 / 0.05 / 0.9

[0103] - Lower layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 95.35 / 0.5 / 1.10 / 0.05 / 3.0

[0104]

[0105] Comparative Example 3: Cathode with application of CNF / CMC=3 composition slurry

[0106] A cathode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower layer slurries had the following compositions, and the slurry composition was changed from that of Example 1. The total amount of CMC and CNF in the slurry of one layer was 0.5 wt% (CMC 0.13 wt%, CNF 0.38 wt%), and the weight ratio of CNF to CMC was 3.

[0107] - Upper layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 97.9 / 0.5 / 0.13 / 0.38 / 0.9

[0108] - Lower layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 95.5 / 0.5 / 0.13 / 0.38 / 3.0

[0109]

[0110] Comparative Example 4: Cathode with application of CNF / CMC=3 composition slurry

[0111] A cathode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower layer slurries had the following compositions, and the slurry composition was changed from that of Example 1. The total amount of CMC and CNF in the slurry of one layer was 1 wt% (CMC 0.25 wt%, CNF 0.75 wt%), and the weight ratio of CNF to CMC was 3.

[0112] - Upper layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 97.9 / 0.5 / 0.25 / 0.75 / 0.9

[0113] - Lower layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 95.5 / 0.5 / 0.25 / 0.75 / 3.0

[0114]

[0115] Comparative Example 5: Cathode applied with CNF / CMC=3 composition slurry

[0116] A cathode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower layer slurries had the following compositions, and the slurry composition was changed from that of Example 1. The total amount of CMC and CNF in the slurry of one layer was 1.5 wt% (CMC 0.38 wt%, CNF 1.13 wt%), and the weight ratio of CNF to CMC was 3.

[0117] - Upper layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 97.9 / 0.5 / 0.38 / 1.13 / 0.9

[0118] - Lower layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 95.5 / 0.5 / 0.38 / 1.13 / 3.0

[0119]

[0120] The compositions of Example 1-2 and Comparative Example 1-5 are summarized in Table 1 below.

[0121] Comparative Example 1Example 1Example 2Comparative Example 2Comparative Example 3Comparative Example 4Comparative Example 5CMC & CNF Weight (Wt%) 1.1510.71.150.511.5CNF / CMC Weight Ratio 00.250.750.045333CNF Weight (Wt%) 00.20.30.050.380.751.13CMC Weight (Wt%) 1.150.80.41.100.130.250.38Cumulative Collector Thickness (Cu foil, um) 6666666

[0122] Meanwhile, a sample with a thickness of 14 μm of the current collector (Cu foil) was manufactured as follows.

[0123]

[0124] Example 3: Application of 14 μm Cu foil

[0125] An anode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower slurries had the following composition and a 14 μm thick Cu foil was used as a current collector. The slurry composition was changed from that of Example 1. The total amount of CMC and CNF per slurry layer was 1.0 wt% (CMC 0.8 wt%, CNF 0.2 wt%), and the weight ratio of CNF to CMC was 0.25.

[0126] - Upper layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 97.6 / 0.5 / 0.8 / 0.2 / 0.9

[0127] - Lower layer composition: graphite / conductive material (carbon black) / CMC / CNF / SBR = 95.35 / 0.5 / 0.8 / 0.2 / 3.0

[0128]

[0129] Comparative Example 6: Application of 14㎛ Cu foil

[0130] A negative electrode was manufactured in the same manner as in Comparative Example 1, except that a 14 μm thick Cu foil was used as the current collector.

[0131]

[0132] The compositions of Examples 1 and 3 and Comparative Examples 1 and 6 are summarized in Table 2 below.

[0133] Comparative Example 1 Example 1 Example 3 Comparative Example 6 CMC & CNF Weight (Wt%) 1.15 11 1.15 CNF / CMC Weight Ratio 0 0.25 0.25 0 CNF Weight (Wt%) 0 0.2 0.20 CMC Weight (Wt%) 1.15 0.8 0.8 1.15 Current Collector Thickness (Cu foil, um) 6 6 14 14

[0134] Experimental example: Measurement of the temperature at which thermal wrinkles occur

[0135] The cathodes of manufactured examples 1-3 and comparative examples 1-2 and 6 were measured using the following logic thermal wrinkle occurrence temperature evaluation tool. The measurement results are shown in Table 3 below.

[0136] When evaluating on the manufacturing line, the electrode temperature was first measured inside the drying furnace after electrode coating. A drying zone with the same measured electrode temperature and hot air temperature was identified, and the presence or absence of thermal wrinkles at the drying furnace outlet was confirmed. If thermal wrinkles were detected, the hot air temperature (or electrode temperature) of the designated drying zone was measured as the thermal wrinkle occurrence temperature.

[0137] When evaluating at the lab level, the oven temperature was first set to 40℃, and then the electrodes were coated and dried in the oven. Drying was continued until the electrode temperature reached the oven temperature, and the occurrence of thermal wrinkles was checked within 1 minute of complete drying. If no thermal wrinkles occurred, the oven temperature was increased by 10℃ and the above process was repeated. If thermal wrinkles occurred, the set oven temperature (electrode temperature at the completion of drying) was measured as the thermal wrinkle occurrence temperature.

[0138] Comparative Example 1 Example 1 Example 2 Example 3 Comparative Example 2 Comparative Example 6 Thermal Wrinkle Occurrence Temperature (℃) 60±1080±1090±10120±2060±10100±20 Thermal Wrinkle Improvement Effect -20℃ Improvement 30℃ Improvement -

[0139] Referring to Table 3, in the case of Example 1 having a CNF / CMC weight ratio of 0.25 and Example 2 having a CNF / CMC weight ratio of 0.75, the thermal wrinkle occurrence temperatures are 80±10℃ and 90±10℃, respectively, and in the case of Comparative Example 1 having a CMC-only composition and Comparative Example 2 having a CNF / CMC weight ratio of 0.045, the thermal wrinkle occurrence temperatures are 60±10℃. Based on this, it can be confirmed that Example 1 having a CNF / CMC weight ratio of 0.25 and Example 2 having a CNF / CMC weight ratio of 0.75 have superior thermal wrinkle properties compared to Comparative Example 1 having a CMC-only composition and Comparative Example 2 having a CNF / CMC weight ratio of 0.045. In this case, the thermal wrinkle improvement effect was improved by 20℃ and 30℃ in Examples 1 and 2, respectively.

[0140] In addition, among Comparative Examples 3-5 in which the weight ratio of CNF / CMC was 3, Comparative Example 3-4 was unable to secure electrode slurry dispersibility due to the low CMC ratio, making electrode manufacturing itself impossible. Accordingly, although there are some differences depending on the composition, it can be seen that the CMC content of the entire composition must be 0.4 wt% or more to secure processability. In addition, Comparative Example 4-5 had a high CNF content, which increased the slurry viscosity and caused an uneven coating process, making uniform electrode manufacturing impossible.

[0141] Meanwhile, as the thickness of the Cu foil increased, the temperature at which thermal wrinkles occurred increased in Example 3 and Comparative Example 6, but it was confirmed that the level of thermal wrinkle improvement was similar regardless of the thickness of the Cu foil. Accordingly, it was confirmed that the negative electrode slurry composition according to the present invention has excellent thermal wrinkle characteristics by setting the CNF / CMC weight ratio to a range of about 0.05 to 3.00.

[0142]

[0143] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. Contains a negative active material, a conductive material, and two or more types of cellulose-based binders. The above cellulose-based binder includes carboxymethyl cellulose (CMC) and cellulose nanofibrils (CNF), A negative electrode slurry composition, wherein the weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethyl cellulose (CMC) among the cellulose-based binders (CNF / CMC) is in the range of about 0.05 to 3.

00.

2. In paragraph 1, A cathode slurry composition wherein the fiber width of the above cellulose nanofibrils (CNF) is about 1 nm to 100 nm.

3. In paragraph 2, A cathode slurry composition wherein the fiber length of the above cellulose nanofibrils (CNF) is about 10 nm to 5,000 nm.

4. In paragraph 1, A negative electrode slurry composition, wherein the weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethyl cellulose (CMC) in the binder (CNF / CMC) is in the range of about 0.25 to 0.

75.

5. In paragraph 1, A cathode slurry composition, wherein the cellulose-based binder is included in an amount of about 0.5 to 1.5 wt% based on the total weight of the cathode slurry composition.

6. In paragraph 1, A cathode slurry composition, wherein the cellulose-based binder is included in an amount of about 0.7 to 1.2 wt% based on the total weight of the cathode slurry composition.

7. In paragraph 1, A negative electrode slurry composition, wherein the carboxymethyl cellulose (CMC) is included in an amount of about 0.4 to 1.5 wt% based on the total weight of the composition.

8. In paragraph 1, The composition further comprises at least one non-cellulosic binder selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinylacetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, and mixtures thereof.

9. In paragraph 1, A negative electrode slurry composition wherein the negative electrode active material comprises a carbon-based material, a silicon-based material, or a Si-C composite.

10. In paragraph 1, A cathode slurry composition, wherein the conductive material comprises at least one selected from the group consisting of graphite, carbon black, carbon-based materials, conductive fibers, fluorinated carbon, metal powder, conductive oxides, and conductive polymers.

11. Negative current collector; and A negative electrode active material layer formed on the negative electrode current collector; The above negative electrode active material layer is formed from the negative electrode slurry composition according to claim 1, The above cellulose nanofibrils (CNF) are a negative electrode for a lithium secondary battery that suppresses the occurrence of thermal wrinkles in a negative electrode current collector.

12. In paragraph 11, A negative electrode for a lithium secondary battery, wherein the negative active material layer has a multilayer structure including an upper active material layer and a lower active material layer, and the upper active material layer and the lower active material layer are formed of a negative electrode slurry composition having different compositions.

13. In paragraph 11, A negative electrode for a lithium secondary battery, wherein the weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethyl cellulose (CMC) (CNF / CMC) is in the range of about 0.05 to 3.

0.

14. In paragraph 13, A negative electrode for a lithium secondary battery, wherein the weight ratio of cellulose nanofibrils (CNF) to the weight of carboxymethyl cellulose (CMC) (CNF / CMC) is in the range of about 0.25 to 0.

75.

15. In paragraph 11, A negative electrode for a lithium secondary battery, wherein the negative current collector has a thickness of about 2 ㎛ to 10 ㎛.

16. Containing a positive electrode; a negative electrode; and an electrolyte including a lithium salt and a non-aqueous organic solvent; A lithium secondary battery comprising a negative electrode for a secondary battery according to Article 11 as a negative electrode.