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

Abstract

The present application relates to an anode slurry composition for mitigating thermal wrinkles of an electrode. The composition includes: an anode active material; a conductive material; and two or more types of cellulose-based binders, in which the cellulose-based binders comprise carboxymethyl cellulose (CMC) and cellulose nanofibers (CNF), and the weight ratio (CNF / CMC) of the cellulose nanofibers (CNF) to the carboxymethyl cellulose (CMC) in the cellulose-based binders is in the range of 0.05 to 3.00.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application is based on and claims priority to Korean Patent Application No. 10-2023-0111309 filed with the Korean Intellectual Property Office on August 24, 2023, and Korean Patent Application No. 10-2024-0113026 filed with the Korean Intellectual Property Office on August 22, 2024, the disclosures of which are incorporated herein by reference in their entirety.

[0003] This specification discloses an anode slurry composition, an anode for a lithium secondary battery, and a lithium secondary battery. Background Technology

[0004] Secondary batteries are gaining increasing attention as a power source, not only for small electronic devices such as portable computers, mobile phones, and cameras, but also for large electronic devices such as electric vehicles and energy storage systems.

[0005] These secondary batteries are manufactured, for example, in cylindrical, prismatic, or pouch shapes, and the manufactured batteries are assembled into, for example, battery packs. These battery packs are then used, for example, in electric vehicles or energy storage systems.

[0006] Meanwhile, during battery manufacturing, anodes and cathodes are produced, and separators are inserted between them to form electrode assemblies. Various studies are currently underway on the processes for manufacturing the anodes, cathodes, and separators. Summary of the Invention

[0007] Technical issues

[0008] This disclosure addresses and resolves a process defect that occurs during the drying process after electrode coating, where the electrode temperature rises to the temperature of the drying oven at the end of the drying process, causing the foil to thermally expand. The electrode cannot withstand this expansion, resulting in the formation of cracks.

[0009] Technical solution

[0010] An anode slurry composition according to one embodiment of the present disclosure includes: an anode active material; a conductive material; and two or more types of cellulose-based binders. The cellulose-based binders include carboxymethyl cellulose (CMC) and cellulose nanofibers (CNF), and the weight ratio (CNF / CMC) of cellulose nanofibers (CNF) in the cellulose-based binders is in the range of about 0.05 to 3.00.

[0011] Cellulose nanofibers (CNFs) have a fiber width in the range of about 1 nm to 100 nm and a fiber length in the range of about 10 nm to 5,000 nm.

[0012] The weight ratio (CNF / CMC) of cellulose nanofibers (CNF) to carboxymethyl cellulose (CMC) in the cellulose-based adhesive is in the range of about 0.25 to 0.75.

[0013] The cellulose-based binder is present in an amount ranging from about 0.5% to 1.5% by weight, based on the total weight of the anode slurry composition.

[0014] The cellulose-based binder is present in an amount ranging from about 0.7% to 1.2% by weight, based on the total weight of the anode slurry composition.

[0015] Based on the total weight of the composition, carboxymethyl cellulose (CMC) is present in an amount ranging from about 0.4% to 1.5% by weight.

[0016] The composition further includes one or more non-cellulose-based adhesives selected from the group consisting of: polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, poly(meth)acrylate, polyethylene-(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-butadiene rubber, fluororubber, and mixtures thereof.

[0017] The anode active material includes carbon-based materials, silicon-based materials, or Si-C composite materials.

[0018] The conductive material includes one or more selected from the group consisting of: graphite, carbon black, carbon-based materials, conductive fibers, fluorocarbons, metal powders, conductive oxides, and conductive polymers.

[0019] According to another embodiment of this disclosure, an anode for a lithium secondary battery includes: an anode current collector; and an anode active material layer formed on the anode current collector. The anode active material layer is formed from the aforementioned anode slurry composition, and the cellulose nanofibers (CNF) suppress the occurrence of thermal wrinkling in the anode current collector.

[0020] The anode active material layer of the aforementioned 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 by an anode slurry composition with different compositions.

[0021] The weight ratio (CNF / CMC) of the cellulose nanofibers (CNF) to the carboxymethyl cellulose (CMC) is in the range of 0.05 to 3.0.

[0022] The weight ratio (CNF / CMC) of the cellulose nanofibers (CNF) to the carboxymethyl cellulose (CMC) is in the range of about 0.25 to 0.75.

[0023] The thickness of the anode current collector is in the range of approximately 2 µm to 10 µm.

[0024] A lithium secondary battery according to another embodiment of this disclosure includes: a cathode; an anode; and an electrolyte comprising a lithium salt and a non-aqueous organic solvent. The lithium secondary battery includes the aforementioned anode for lithium secondary batteries as the anode.

[0025] Beneficial effects

[0026] The anode slurry composition according to embodiments of this disclosure can minimize thermal wrinkling that occurs during the drying process after electrode coating in the manufacturing process using relatively thin foil as the electrode for current collectors. As a result, electrode productivity during the manufacturing process can be improved, and the energy density of the manufactured battery can also be increased. Detailed Implementation

[0027] In the following, for example, an electrolyte composition for a lithium metal battery according to an embodiment of the present disclosure will be described.

[0028] The terms and words used in the specification and claims should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical ideas of this disclosure, based on the principle that the inventor can appropriately define the concepts of the terms in order to interpret his or her invention in the best possible way.

[0029] The terminology used herein is for describing exemplary embodiments only and is not intended to limit the scope of this disclosure. Unless the context clearly indicates otherwise, singular terms include plural terms.

[0030] As used herein, terms such as “comprising,” “including,” and “having” are used to indicate the presence of features, numbers, steps, components, and / or combinations thereof, but should not be construed as precluding the possibility of the presence or addition of one or more other features, numbers, steps, components, and / or combinations thereof.

[0031] As used herein, taking into account the inherent tolerances in manufacturing and materials, the terms “approximately,” “about,” and “substantially” are understood to refer to a range or approximation of a numerical or degree of value.

[0032] In this specification, "heat wrinkling temperature" refers to the temperature of the drying oven where heat wrinkling occurs.

[0033] In battery manufacturing, electrode manufacturing involves coating electrode material onto a current collector and then drying it. For example, during electrode drying, wrinkles may form on the foil-like current collector supporting the electrodes in the drying oven, and cracks may appear in the electrodes. This phenomenon is called heat wrinkle. This is a process defect that occurs during the drying process after electrode coating on the current collector, and it primarily occurs at the anode. Heat wrinkle is caused by the difference in thermal expansion coefficients between the electrode and the foil. This is because at the end of the drying process, the electrode temperature rises to the temperature of the drying oven, causing the current collector foil to thermally expand. The electrode cannot withstand this thermal expansion, leading to cracks in the electrode.

[0034] This thermal wrinkling phenomenon tends to become more severe as the drying temperature increases and the foil thickness decreases.

[0035] Meanwhile, the battery industry has recently been trending towards increasing drying speed and oven temperature to improve electrode productivity, while reducing foil thickness to increase battery energy density, thereby increasing the likelihood of thermal wrinkling in the manufacturing process.

[0036] This disclosure provides an anode slurry composition that minimizes thermal wrinkling in the electrode even in harsh environments, an anode for a lithium secondary battery, and a lithium secondary battery including the anode.

[0037] Anode slurry composition

[0038] According to one embodiment of this disclosure, an anode slurry composition is provided, comprising: an anode active material; a conductive material; and two or more types of cellulose-based binders. The cellulose-based binders comprise carboxymethyl cellulose (CMC) and cellulose nanofibers (CNF), and the weight ratio (CNF / CMC) of cellulose nanofibers (CNF) in the cellulose-based binder is in the range of 0.05 to 3.00.

[0039] This anode slurry composition can specifically include cellulose nanofibers (CNF) as a cellulose-based binder, thereby suppressing thermal wrinkling in the anode current collector. Furthermore, by applying carboxymethyl cellulose (CMC) and cellulose nanofibers (CNF) in a specific weight ratio as a cellulose-based binder, the level of thermal wrinkling occurrence can be improved (e.g., suppressed). According to one embodiment, the fiber width of the cellulose nanofibers (CNF) is in the range of about 1 nm to 100 nm, for example, in the range of about 3 nm to 10 nm. The fiber length of the cellulose nanofibers (CNF) is in the range of about 110 nm to 5,000 nm, for example, in the range of about 100 nm to 2,000 nm. The fiber width and length of these cellulose nanofibers (CNF) can be measured using AFM, SEM, and TEM.

[0040] For example, the weight ratio (CNF / CMC) of cellulose nanofibers (CNF) to carboxymethyl cellulose (CMC) in a cellulose-based binder can be in the range of about 0.05 to 3.00 or about 0.1 to 1.0. According to one embodiment, the weight ratio (CNF / CMC) can be in the range of about 0.25 to 0.75. When the above weight ratio range is met, the level of thermal wrinkling can be suppressed, thereby providing an advantage in electrode production yield.

[0041] In an exemplary embodiment, the cellulose-based binder may be included in an amount ranging from about 0.5% to 1.5% by weight, based on the total weight of the anode slurry composition. For example, the cellulose-based binder may be included in an amount ranging from about 0.7% to 1.2% by weight, based on the total weight of the anode slurry composition. When the cellulose-based binder content falls within the above range, the level of thermal wrinkling can be significantly suppressed.

[0042] In an exemplary embodiment, carboxymethyl cellulose (CMC) may be included in an amount ranging from about 0.4% to 1.5% by weight, based on the total weight of the composition. For example, when the carboxymethyl cellulose content is less than about 0.4% by weight, the low CMC ratio may make it difficult to achieve good dispersibility of the electrode slurry, and thus may not ensure processing performance.

[0043] Meanwhile, based on the total weight of the composition, the CNF content can be less than or equal to about 0.4% by weight. In particular, when the CNF content is too high compared to 0.4% by weight, the slurry viscosity may increase, leading to coating process defects, which may be detrimental to the uniform production of electrodes.

[0044] In an exemplary embodiment, in addition to two or more types of cellulose adhesives, the composition may further include a non-cellulose-based adhesive. The aforementioned non-cellulose-based adhesives are components that facilitate the bonding of anolyl active materials and conductive materials, as well as their bonding to current collectors. For example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, poly(meth)acrylate, poly(ethyl)methacrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butadiene rubber, fluororubber, and mixtures thereof can be used as a non-cellulose adhesive. However, non-cellulose-based adhesives are not necessarily limited to this.

[0045] Based on 100 parts by weight of the total anode weight, the content of the aforementioned non-cellulose-based binder can range from about 1 part by weight to 50 parts by weight, or from about 3 parts by weight to 15 parts by weight. As a result, the bonding strength between the anode active material and the current collector, as well as the capacity characteristics of the secondary battery, can be maintained.

[0046] In exemplary embodiments, the aforementioned anodic active material may include carbon-based materials, silicon-based materials, or Si-C composite materials. For example, compounds capable of reversibly inserting and de-intercalating lithium can be used as anodic active materials. According to one embodiment, the following materials can be used as anodic active materials: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, or amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Sb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides capable of doping and de-doping lithium, such as SiO2. β (0 < β < 2), SnO2, vanadium oxide or lithium vanadium oxide; or composite materials including the above-mentioned metal compounds and carbonaceous materials, such as Si-C composite materials or Sn-C composite materials, and one or more of these materials or mixtures thereof. In addition, thin films of metallic lithium can be used as anode active materials.

[0047] For the aforementioned carbonaceous materials, both low-crystallinity carbon and high-crystallinity carbon can be used. Soft carbon and hard carbon are representative examples of low-crystallinity carbon. High-crystallinity carbon can be achieved using the following materials: amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbicads, mesophase pitches, and high-temperature calcined carbon, such as petroleum or coal tar pitch-derived cokes.

[0048] In an exemplary embodiment, the conductive material may include at least one selected from the group consisting of graphite, carbon black, carbonaceous materials, conductive fibers, fluorocarbons, metal powders, conductive oxides, and conductive polymers.

[0049] For example, conductive materials included in the anode can be used, provided they do not cause side reactions in the internal environment of the lithium secondary battery, do not cause chemical changes within the battery, and have improved conductivity. In one embodiment, graphite or conductive carbon can be used. For example, the following materials can be used alone or in combination of two or more: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, or lamp black; carbon-based materials having a graphene or graphite crystal structure; conductive fibers, such as carbon fibers or metal fibers; fluorinated carbon; metal powders, such as aluminum or nickel powder; conductive oxides, such as titanium dioxide; and conductive polymers, such as polyphenylene derivatives. However, graphite or conductive carbon is not limited to these.

[0050] Based on 100 parts by weight of the total weight of the anode, the content of conductive material can range from about 0.5 parts by weight to 50 parts by weight, or from about 1 part by weight to 30 parts by weight. As a result, the electrochemical properties of the anode and the lithium secondary battery, such as conductivity and capacity, can be maintained.

[0051] Anodes for lithium secondary batteries and lithium secondary batteries

[0052] According to another embodiment of this disclosure, an anode for a lithium secondary battery includes: an anode current collector; and an anode active material layer formed on the anode current collector. The anode active material layer is formed from the aforementioned anode slurry composition, and the cellulose nanofibers (CNF) suppress the occurrence of thermal wrinkling in the anode current collector.

[0053] In one exemplary embodiment, the anode can be manufactured according to conventional methods known in the art. For example, an anode active material, a conductive material, a binder, and, if necessary, a filler can be dispersed and mixed in a dispersion medium (solvent) to prepare a slurry, which can be applied to an anode current collector and then dried and rolled to manufacture the anode. The slurry can be applied to the anode current collector using, for example, a single-layer die coating (SLD) method.

[0054] In one exemplary embodiment, the anolyte active material layer has a multilayer structure comprising an upper active material layer and a lower active material layer, and the upper and lower active material layers can be formed from anolyte slurry compositions with different compositions. For example, at least one of the upper and lower active material layers can be formed using the anolyte slurry composition detailed above. This multilayer structure can be manufactured by coating and drying using a double-layer die coating (DLD) method in a wet-on-wet manner. On the other hand, an anolyte active material layer having a single-layer structure can be manufactured by coating and drying using a single-layer die coating (SLD) method.

[0055] In one exemplary embodiment, the weight ratio of cellulose nanofibers (CNF) to carboxymethyl cellulose (CMC) (CNF / CMC) can be in the range of about 0.05 to 3.0. For example, the weight ratio of cellulose nanofibers (CNF) to carboxymethyl cellulose (CMC) (CNF / CMC) can be in the range of about 0.25 to 0.75. When the above weight ratio range is met, the level of thermal wrinkling can be suppressed, thereby providing an advantage in electrode production yield.

[0056] In one exemplary embodiment, the anode current collector described above may be made of, but is not limited to, the following materials: 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 anode current collector may be in the form of, for example, foil, film, sheet, perforated form, porous body, or foam.

[0057] In one exemplary embodiment, the thickness of the anode current collector can range from about 2 µm to 10 µm. For example, the thickness of the anode current collector can range from about 4 µm to 8 µm. While applying thin current collectors to improve the energy density of the battery, the possibility of thermal wrinkling during manufacturing can be significantly reduced by introducing the anode slurry composition according to embodiments of the present disclosure.

[0058] According to another embodiment of this disclosure, a lithium secondary battery is provided, comprising a cathode, an anode, and an electrolyte, the electrolyte comprising a lithium salt and a non-aqueous organic solvent, and including the anode for the secondary battery as the anode.

[0059] In one exemplary embodiment, the cathode described above can be manufactured, for example, by dispersing and mixing a cathode active material, a binder, and a conductive material in a dispersion medium (solvent) to prepare a slurry, applying the slurry to a cathode current collector, and then drying and rolling it. In this case, N-methyl-2-pyrrolidone (NMP), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), ethanol, isopropanol, water, and mixtures thereof can be used as the dispersion medium, but are not necessarily limited to these.

[0060] The aforementioned cathode current collector can be made of, but is not limited to, the following materials: 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 their alloys, as well as aluminum (Al) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The cathode current collector can be, for example, in the form of foil, film, sheet, perforated form, porous body, or foam.

[0061] Meanwhile, in other embodiments of lithium secondary batteries, the cathode active material is not particularly limited, as long as it is a material capable of reversibly inserting and extracting lithium ions, and may include, for example, lithium metal composite oxides, which include at least one metallic element selected from the group consisting of Co, Mn, Ni, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg and Mo.

[0062] According to one embodiment, for the cathode active material, a compound represented by any of the following chemical formulas can be used. Li aA 1-b R b D2 (where 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b R b O 2-c D c (Where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE 2-b R b O 4-c D c (where 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b R c D α (Where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); Li a Ni 1-b-c Co b R c O 2-α Zα (where 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 (where 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 (Where 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 (Where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni 1-b- c Mn bR c O 2-α Z2 (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α < 2); Li a Ni b E c G d O2 (where 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 G e O2 (where 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1); Li a NiG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a C o G b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (where 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiTO2; LiNiVO4; and Li (3-f) J2(PO4)3 (0 ≤ f ≤ 2).

[0063] In the above chemical formulas, A is Ni, Co, Mn or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, V or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0064] In addition to the cathode active material described above, the cathode may further include, for example, a binder and a conductive material. Furthermore, the same binder and conductive material described for the anode can be used as well, therefore, further description in this regard will be omitted.

[0065] Fillers can be optionally added to the cathode as a component to suppress its expansion. There are no particular limitations on the fillers, as long as they suppress the expansion of the electrode without causing chemical changes in the cell. For example, olefin polymers such as polyethylene or polypropylene, or fibrous materials such as glass fiber or carbon fiber, can be used.

[0066] The lithium secondary battery described in other embodiments above may include an electrolyte comprising a lithium salt and a non-aqueous organic solvent. The electrolyte acts as a medium for transporting lithium ions between the cathode and anode. Lithium ions may exist in the electrolyte in a solvated state and may be inserted into the electrode active material through desolvation at the electrolyte-electrode interface.

[0067] The lithium salt included in the electrolyte serves as a medium for transporting ions within the lithium secondary battery. The lithium salt contains, for example, Li. + As a cation, and may contain F-selected - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO2 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3 - (CF3CF2SO2)2N - 、(CF3SO 2)2 N - (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 - The anions in the group.

[0068] According to one embodiment, the lithium salt may include, selected from LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 At least one of the following groups: 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, LiTFSI (lithium bis(trifluoromethanesulfonyl) imide), and LiN(SO2CF3)2.

[0069] The concentration of lithium salts can be appropriately varied within the generally available range and can be included in the electrolyte in a concentration range of about 0.5 M to 6 M or 1 M to 5 M.

[0070] In one embodiment, the electrolyte may comprise a relatively low concentration of lithium salt, approximately 0.5 M to less than 2 M, or approximately 0.7 M to 1.5 M. Even in this case, the lithium secondary battery of other embodiments can exhibit improved output characteristics because the electrode in the above embodiments accelerates the desolvation of lithium ions.

[0071] Furthermore, in another embodiment of this disclosure, the electrolyte may contain a high-concentration lithium salt in the range of about 2 M to 6 M or about 2.5 M to 5.5 M. In this case, by including a high-concentration lithium salt and applying the electrode in this embodiment, the desolvation of lithium ions can be further accelerated, and the output characteristics of the secondary battery can be further improved.

[0072] Furthermore, there are no particular limitations on the types of non-aqueous organic solvents that may be included in the electrolyte; any organic solvent known to be suitable for electrolytes such as lithium-ion batteries may 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] According to one embodiment, as a carbonate solvent, for example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate, methyl propyl carbonate, methyl ethyl carbonate, ethyl propyl carbonate, or (2,2,2-trifluoroethyl)methyl carbonate can be used. As a phosphate ester solvent, for example, trimethyl phosphate, triethyl phosphate, or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxophosphazenecyclohexane 2-oxide can be used.

[0074] As an ether solvent, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, or tetrahydrofuran derivatives, such as 2-methyltetrahydrofuran, can be used. As a nitrile solvent, for example, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile can be used. Furthermore, as a sulfone solvent, for example, dimethyl sulfone, ethylmethyl sulfone, or sulforane can be used.

[0075] In addition to the lithium salt and non-aqueous organic solvents mentioned above, the electrolyte may further include a diluent whose solubility for the lithium salt is at least 10 times less than that for the non-aqueous organic solution. This diluent may be an organic solvent miscible with the non-aqueous organic solvent while exhibiting essentially no solubility for the lithium salt. For example, the diluent may be an ether solvent having a fluorinated alkyl group. For instance, the diluent may include one or more 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), methylnonafluorobutane (MOFB), and ethylnonafluorobutane (EOFB).

[0076] When this diluent is further included, the high-concentration lithium salt may be locally present in the non-aqueous organic solvent within the electrolyte, while the lithium salt may not be substantially present in the diluent. Thus, since the high-concentration lithium salt is locally present in the electrolyte in a solvated form, the output characteristics of the lithium secondary battery can be further improved, while reducing the increase in electrolyte viscosity and the decrease in fluidity. Furthermore, when the electrode of the embodiment is used with this high-concentration salt electrolyte, lithium-ion conductivity can be improved and resistance can be reduced, even at relatively low temperatures. As a result, the degradation of low-temperature output characteristics due to, for example, the high concentration of lithium salt can be reduced.

[0077] The amount of diluent can be adjusted according to the type of non-aqueous organic solvent and the type or total concentration of lithium salt. For example, the diluent can be included in the electrolyte at a molar ratio of about 1:0.2 to 1:5, or about 1:0.5 to 1:2, with the non-aqueous organic solvent.

[0078] Additionally, the lithium secondary battery of other embodiments described above may further include a porous separator inserted between the cathode and the anode.

[0079] Porous separators can be made from olefin polymers such as polyethylene and polypropylene, or glass fibers, in the form of sheets, multilayer membranes, microporous membranes, fabrics, or nonwovens, but are not necessarily limited to these. However, porous polyethylene or porous glass fiber (glass filter) nonwovens can be used as separators, as can porous glass filters. Separators can be insulating films with high ion permeability and mechanical strength. The pore size of the separator is typically in the range of about 0.01 μm to 10 μm, and the thickness is typically in the range of about 5 μm to 300 μm, but is not limited to these.

[0080] Furthermore, in another example of a lithium secondary battery, a separator may not be inserted, and the electrolyte may be inserted between the cathode and anode 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 aforementioned lithium salt and non-aqueous organic solvent; for example, a known polymer-based solid electrolyte may be used as the polymer matrix. In this case, the lithium secondary battery in the other embodiments described above may be a semi-solid-state battery using a combination of liquid electrolyte and solid electrolyte.

[0081] Furthermore, lithium secondary batteries in other embodiments can be manufactured according to conventional methods in the art. For example, a lithium secondary battery can be manufactured by housing an electrode assembly including a cathode, an anode, and a separator (or an electrolyte membrane) within a casing and injecting and impregnating the electrolyte described above.

[0082] This type of lithium secondary battery can be used not only as a battery cell for powering small devices, but is also particularly suitable as a cell battery for battery modules for powering medium and large devices.

[0083] Embodiments of this disclosure will be described in detail below to enable those skilled in the art to readily implement this disclosure. However, this disclosure can be implemented in many different forms and is not limited to the embodiments described herein.

[0084] Comparative Example 1: Anode coated with a slurry containing only CMC

[0085] The anode paste was coated onto a 6 μm thick copper foil using a wet-on-wet double-layer die coating (DLD) method and then dried to fabricate the electrode. The upper and lower layers each contained 130 ± 20 mg / 25 cm⁻¹ of paste. 2 The load resulted in a final coating thickness of 260 ± 20 mg / 25 cm on the copper foil. 2 The composition of the upper and lower slurry layers is as follows. At this point, the CMC content of both the upper and lower layers is 1.15% by weight.

[0086] - Upper layer composition: Graphite / Conductive material (carbon black) / CMC / SBR = 97.45 / 0.5 / 1.15 / 0.9

[0087] - Lower layer composition: Graphite / Conductive material (carbon black) / CMC / SBR = 95.35 / 0.5 / 1.15 / 3.0

[0088] Example 1: Anode coated with a CNF / CMC = 0.25 composition slurry

[0089] The anode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower slurries had the following composition. The total amount of CMC and CNF in any layer of the slurry was 1.0 wt% (CMC 0.8 wt%, CNF 0.2 wt%), and the weight ratio of CNF to CMC was 0.25.

[0090] - Upper layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 97.6 / 0.5 / 0.8 / 0.2 / 0.9

[0091] - Lower layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 95.35 / 0.5 / 0.8 / 0.2 / 3.0

[0092] Example 2: Anode coated with a CNF / CMC = 0.75 composition slurry

[0093] The anode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower slurries had the following composition. The slurry composition was modified from that of Example 1 above. The total amount of CMC and CNF in any layer of the slurry was 0.7% by weight (0.4% by weight of CMC and 0.3% by weight of CNF), and the weight ratio of CNF to CMC was 0.75.

[0094] - Upper layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 97.9 / 0.5 / 0.4 / 0.3 / 0.9

[0095] - Lower layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 95.5 / 0.5 / 0.4 / 0.3 / 3.0

[0096] Comparative Example 2: Anode coated with a CNF / CMC = 0.045 composition slurry

[0097] The anode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower slurries had the following composition. The total amount of CMC and CNF in any layer of the slurry was 1.15% by weight (CMC 1.10% by weight, CNF 0.05% by weight), and the weight ratio of CNF to CMC was 0.045.

[0098] - Upper layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 97.45 / 0.5 / 1.10 / 0.05 / 0.9

[0099] - Lower layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 95.35 / 0.5 / 1.10 / 0.05 / 3.0

[0100] Comparative Example 3: Anode coated with a CNF / CMC = 3 composition slurry

[0101] The anode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower slurries had the following composition, which was modified from the slurry composition in Example 1. The total amount of CMC and CNF in either layer of the slurry was 0.5% by weight (0.13% by weight of CMC and 0.38% by weight of CNF), and the weight ratio of CNF to CMC was 3.

[0102] - Upper layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 97.9 / 0.5 / 0.13 / 0.38 / 0.9

[0103] - Lower layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 95.5 / 0.5 / 0.13 / 0.38 / 3.0

[0104] Comparative Example 4: Anode coated with a CNF / CMC = 3 composition slurry

[0105] The anode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower slurries had the following composition, which was modified from the slurry composition in Example 1. The total amount of CMC and CNF in either layer of the slurry was 1% by weight (0.25% by weight of CMC and 0.75% by weight of CNF), and the weight ratio of CNF to CMC was 3.

[0106] - Upper layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 97.9 / 0.5 / 0.25 / 0.75 / 0.9

[0107] - Lower layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 95.5 / 0.5 / 0.25 / 0.75 / 3.0

[0108] Comparative Example 5: Anode coated with a CNF / CMC = 3 composition slurry

[0109] The anode was manufactured in the same manner as in Comparative Example 1, except that the upper and lower slurries had the following composition, which was modified from the slurry composition in Example 1. The total amount of CMC and CNF in any layer of the slurry was 1.5% by weight (CMC 0.38% by weight, CNF 1.13% by weight), and the weight ratio of CNF to CMC was 3.

[0110] - Upper layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 97.9 / 0.5 / 0.38 / 1.13 / 0.9

[0111] - Lower layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 95.5 / 0.5 / 0.38 / 1.13 / 3.0

[0112] The composition of Examples 1 and 2 and Comparative Examples 1 to 5 is summarized in Table 1 below.

[0113] [Table 1]

[0114]

[0115] The sample preparation of a current collector (copper foil) with a thickness of 14 µm is as follows.

[0116] Example 3: Application of 14 µm copper foil

[0117] The anode was prepared in the same manner as in Comparative Example 1, except that the upper and lower slurries had the following compositions, and a 14 µm thick copper foil was used as the current collector. This slurry composition was modified from that in Example 1. The total amount of CMC and CNF in any layer of the slurry was 1.0 wt% (CMC 0.8 wt%, CNF 0.2 wt%), and the CNF to CMC weight ratio was 0.25.

[0118] - Upper layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 97.6 / 0.5 / 0.8 / 0.2 / 0.9

[0119] - Lower layer composition: Graphite / Conductive material (carbon black) / CMC / CNF / SBR = 95.35 / 0.5 / 0.8 / 0.2 / 3.0

[0120] Comparative Example 6: Application of 14 µm copper foil

[0121] The anode was manufactured in the same manner as in Comparative Example 1, except that a 14 µm thick copper foil was used as the current collector.

[0122] The composition of Examples 1 and 3, and Comparative Examples 1 and 6 is summarized in Table 2 below.

[0123] [Table 2]

[0124]

[0125] Experimental Example: Measurement of the Temperature at which Thermal Wrinkles Occur

[0126] The thermal wrinkling temperature of the anodes manufactured in Examples 1 to 3 and Comparative Examples 1, 2 and 6 was measured using a thermal wrinkling temperature evaluation tool with the following logic. The measurement results are shown in Table 3 below.

[0127] During evaluation on the production line, the electrode temperature inside the drying oven was first measured after electrode coating. A drying zone was designated where the measured electrode temperature and hot air temperature were the same, and the appearance of thermal wrinkles at the oven outlet was confirmed. When thermal wrinkles were observed, the hot air temperature (or electrode temperature) of the previously confirmed drying zone was measured (e.g., recorded) as the thermal wrinkle initiation temperature.

[0128] During laboratory-scale evaluation, the oven temperature (e.g., drying furnace) is first set to 40°C, and the electrode is dried in the oven after coating. The electrode is dried until its temperature reaches the oven temperature, and the appearance of thermal wrinkles is checked within 1 minute after drying is complete. If no thermal wrinkles are observed, the oven temperature is increased by 10°C, and the above process is repeated. When thermal wrinkles are observed, the set oven temperature (e.g., the electrode temperature at the end of drying) is measured as the wrinkle initiation temperature.

[0129] [Table 3]

[0130]

[0131] Referring to Table 3, in Example 1, which contained a CNF / CMC weight ratio of 0.25, and in Example 2, which contained a CNF / CMC weight ratio of 0.75, the thermal wrinkling temperatures were 80 ± 10 °C and 90 ± 10 °C, respectively. In contrast, in Comparative Example 1, which contained only CMC, and Comparative Example 2, which contained a CNF / CMC weight ratio of 0.045, the thermal wrinkling temperature was 60 ± 10 °C. Based on this, it can be determined that, compared to Comparative Example 1, which contained only CMC, and Comparative Example 2, which contained a CNF / CMC weight ratio of 0.045, Examples 1 and 2, which contained a CNF / CMC weight ratio of 0.25, exhibited superior thermal wrinkling suppression properties. In these cases, the thermal wrinkling suppression effect in Examples 1 and 2 was improved by 20 °C and 30 °C, respectively.

[0132] Furthermore, in Comparative Examples 3 to 5, where the CNF / CMC weight ratio was 3, the electrode slurry dispersion was not achieved in Comparative Examples 3 and 4 due to the low CMC content, making electrode fabrication impossible. Therefore, although there are some differences depending on the composition, it can be seen that a CMC content of at least 0.4% by weight is required in the overall composition to ensure processing performance. Additionally, in Comparative Examples 4 and 5, the high CNF content increased the slurry viscosity, leading to coating process defects that prevented the fabrication of uniform electrodes.

[0133] Furthermore, the thermal wrinkling temperature in Examples 3 and 6 increased with increasing copper foil thickness. However, it was confirmed that the thermal wrinkling suppression level remained similar regardless of the copper foil thickness. Therefore, it was confirmed that the anolyte composition according to this disclosure exhibits excellent anti-wrinkle properties when the CNF / CMC weight ratio is in the range of about 0.05 to 3.00.

[0134] In the foregoing, embodiments of this disclosure have been described in detail with reference to exemplary embodiments, but the scope of this disclosure is not limited thereto. Various changes and modifications made by those skilled in the art using the basic concepts of this disclosure as defined in the appended claims also fall within the scope of this disclosure.

Claims

1. An anode slurry composition, comprising: an anode active material; a conductive material; and two or more types of cellulose-based binders, wherein the cellulose-based binders include carboxymethyl cellulose (CMC) and cellulose nanofiber (CNF), and wherein a weight ratio (CNF / CMC) of the cellulose nanofiber (CNF) to the carboxymethyl cellulose (CMC) in the cellulose-based binders is in a range of about 0.05 to 3.

00.

2. The anode slurry composition of claim 1, wherein a fiber width of the cellulose nanofiber (CNF) is in a range of about 1 nm to 100 nm.

3. The anode slurry composition of claim 2, wherein a fiber length of the cellulose nanofiber (CNF) is in a range of about 10 nm to 5,000 nm.

4. The anode slurry composition of claim 1, wherein a weight ratio (CNF / CMC) of the cellulose nanofiber (CNF) to the carboxymethyl cellulose (CMC) in the cellulose-based binders is in a range of about 0.25 to 0.

75.

5. The anode slurry composition of claim 1, wherein the cellulose-based binders are present in an amount in a range of about 0.5 wt% to 1.5 wt% based on a total weight of the anode slurry composition.

6. The anode slurry composition of claim 1, wherein the cellulose-based binders are present in an amount in a range of about 0.7 wt% to 1.2 wt% based on a total weight of the anode slurry composition.

7. The anode slurry composition of claim 1, wherein the carboxymethyl cellulose (CMC) is present in an amount in a range of about 0.4 wt% to 1.5 wt% based on a total weight of the composition.

8. The anode slurry composition of claim 1, further comprising: one or more non-cellulose-based binders selected from the group consisting of: polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, poly(methyl) methyl acrylate, polyethylene-(methyl) acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinyl pyridine, polyvinyl pyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butadiene rubber, fluoroelastomer, and mixtures thereof.

9. The anode slurry composition of claim 1, wherein the anode active material includes a carbon-based material, a silicon-based material, or a Si-C composite material.

10. The anode slurry composition of claim 1, wherein the conductive material includes one or more selected from the group consisting of graphite, carbon black, carbon-based material, conductive fiber, fluorinated carbon, metal powder, conductive oxide, and conductive polymer.

11. An anode for a lithium secondary battery, the anode comprising: an anode current collector; and an anode active material layer formed on the anode current collector, wherein the anode active material layer is formed from the anode slurry composition of claim 1, and wherein the cellulose nanofiber (CNF) suppresses thermal creasing in the anode current collector.

12. The anode of claim 11, wherein the anode active material layer has a multi-layer structure comprising an upper active material layer and a lower active material layer, and wherein the upper active material layer and the lower active material layer are formed from anode slurry compositions having different compositions.

13. The anode of claim 11, wherein a weight ratio of the cellulose nanofiber (CNF) to the carboxymethyl cellulose (CMC) (CNF / CMC) is in a range of 0.05 to 3.

0.

14. The anode of claim 13, wherein a weight ratio of the cellulose nanofiber (CNF) to the carboxymethyl cellulose (CMC) (CNF / CMC) is in a range of about 0.25 to 0.

75.

15. The anode of claim 11, wherein a thickness of the anode current collector is in a range of about 2 µm to 10 µm.

16. A lithium secondary battery comprising: a cathode; an anode; and an electrolyte comprising a lithium salt and a non-aqueous organic solvent, wherein the lithium secondary battery comprises the anode for lithium secondary batteries of claim 11 as the anode.

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