Anode slurry, anode for lithium secondary battery, and lithium secondary battery comprising same

Abstract

According to embodiments of the present disclosure, the aqueous anode slurry may comprise an anode active material, a binder, and an organic acid compound that has at least two oxygen-containing functional groups. In a molecular structure of the organic acid compound, the bonding angle between the oxygen-containing functional groups is 90<sb / > o or greater, and the amount of organic acid compound can be greater than 0.01 wt% and less than 0.1 wt% on the basis of the total weight of a solid part of the aqueous anode slurry.

Description

Negative electrode slurry, negative electrode for lithium secondary battery, and lithium secondary battery containing same

[0001] The present disclosure relates to a negative electrode slurry, a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode for the lithium secondary battery.

[0002]

[0003] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as hybrid vehicles.

[0004] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. The high operating voltage and energy density per unit weight of lithium secondary batteries can be advantageous for increasing charging speed and reducing weight.

[0005] A lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator. For example, the positive electrode and the negative electrode may be formed by coating an electrode forming composition on an electrode current collector such as a metal foil. The electrode forming composition may be prepared by mixing an electrode active material, a binder, and a solvent, and may have, for example, a slurry form.

[0006] Recently, as the applications of lithium secondary batteries have expanded, higher capacity and output characteristics are required. Furthermore, lithium secondary batteries must operate stably even under harsh conditions, depending on the usage environment. Therefore, cycle characteristics and stability must be considered along with high capacity and output.

[0007]

[0008] An object of the present disclosure is to provide a cathode slurry providing improved electrochemical properties and stability.

[0009] An object of the present disclosure is to provide a negative electrode for a lithium secondary battery having improved electrochemical properties and stability.

[0010] An object of the present disclosure is to provide a lithium secondary battery having improved electrochemical properties and stability.

[0011]

[0012] The aqueous negative electrode slurry according to embodiments of the present disclosure may include a negative electrode active material, a binder, and an organic acid compound having at least two oxygen-containing functional groups. In the molecular structure of the organic acid compound, the bond angle between the oxygen-containing functional groups is 90. o It may be ideal. The content of the organic acid compound may be more than 0.01 wt% and less than 0.1 wt% of the total solid weight of the aqueous cathode slurry.

[0013] In some embodiments, the binder may include carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (Na-carboxymethyl cellulose), lithium carboxymethyl cellulose (Li-carboxymethyl cellulose), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyacrylamide (PAM), or a copolymer thereof.

[0014] In one embodiment, the binder may comprise polyvinyl alcohol, polyacrylic acid, polyacrylamide, or a copolymer thereof.

[0015] In some embodiments, the negative active material may include a silicon-containing material.

[0016] In some embodiments, the oxygen-containing functional group may include an aldehyde group, a carboxyl group, or a hydroxy group linked to a carbon atom that does not form a pi (π) bond with an oxygen atom.

[0017] In one embodiment, the bond angle between the oxygen-containing functional groups may be the internal angle between the bond lines connecting the oxygen-containing functional group and the carbon atom bonded to the oxygen-containing functional group in the molecular structure of the organic acid compound.

[0018] In one embodiment, the organic acid compound may include at least one acid compound selected from the group consisting of lactic acid, glycolic acid, succinic acid, fumaric acid, malonic acid, glutaric acid, adipic acid, pimelic acid, and oxalic acid.

[0019] In one embodiment, the organic acid compound may include at least one acid compound selected from the group consisting of lactic acid, fumaric acid, succinic acid, and oxalic acid.

[0020] In some embodiments, the organic acid compound may have two or three oxygen-containing functional groups.

[0021] In some embodiments, the content of the organic acid compound may be 0.02 wt% to 0.08 wt% of the total solid weight of the aqueous cathode slurry.

[0022] In one embodiment, the aqueous cathode slurry may further comprise an aqueous solvent.

[0023] In some embodiments, the pH of the aqueous cathode slurry may be 8 or less.

[0024] The negative electrode for a lithium secondary battery according to embodiments of the present disclosure may include a negative electrode active material, a binder, and a negative electrode active material layer including an organic acid compound having at least two oxygen-containing functional groups. In the molecular structure of the organic acid compound, a bond angle between the oxygen-containing functional groups is 90. o In addition, the content of the organic acid compound may be more than 0.01 wt% and less than 0.1 wt% of the total weight of the negative electrode active material layer.

[0025] In some embodiments, the organic acid compound may be cross-linked with the binder.

[0026] In some embodiments, the negative electrode for the lithium secondary battery may further include a negative electrode current collector. The negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector.

[0027] In one embodiment, the adhesive force between the negative electrode active material layer and the negative electrode current collector may be 0.5 N / 18 mm or more.

[0028] A lithium secondary battery according to embodiments of the present disclosure may include a negative electrode for a lithium secondary battery according to the embodiments described above, and a positive electrode facing the negative electrode for a lithium secondary battery.

[0029]

[0030] According to embodiments of the present disclosure, an aqueous cathode slurry may include an organic acid compound having at least two oxygen-containing functional groups and a specific molecular structure. The aqueous cathode slurry may have improved coatability, and the ionic conductivity of the aqueous cathode slurry may be improved.

[0031] The negative electrode for a lithium secondary battery may include the organic acid compound described above. The content of the organic acid compound in the aqueous negative electrode slurry or the negative electrode for a lithium secondary battery may be adjusted within a predetermined range. The negative electrode for a lithium secondary battery may have low resistance without a decrease in energy density, and the high-temperature stability of the negative electrode for a lithium secondary battery may be improved.

[0032] A lithium secondary battery may include the above-described negative electrode for a lithium secondary battery. The internal resistance of the lithium secondary battery may be reduced, and the capacity, life characteristics, and stability may be improved.

[0033]

[0034] FIG. 1 and FIG. 2 are schematic plan views and cross-sectional views, respectively, showing lithium secondary batteries according to exemplary embodiments.

[0035]

[0036] According to embodiments of the present disclosure, the aqueous cathode slurry may include a cathode active material, a binder, and an organic acid compound.

[0037] According to embodiments of the present disclosure, a negative electrode for a lithium secondary battery may include a negative electrode active material, a binder, and an organic acid compound. According to embodiments of the present disclosure, a lithium secondary battery may include the above-described negative electrode for a lithium secondary battery.

[0038] Lithium secondary batteries according to embodiments of the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, lithium secondary batteries according to embodiments of the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, and other vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0039] The terms “top surface”, “bottom surface”, etc. used in this disclosure indicate the relative positions of each component and do not imply an absolute superior-subordinate relationship.

[0040] Below, the present disclosure will be described in detail. However, this is merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0041] The cathode slurry according to exemplary embodiments may include a cathode active material, a binder, and an organic acid compound.

[0042] In one embodiment, the cathode slurry may further comprise a solvent. The solvent may be an aqueous solvent. For example, the cathode slurry may be an aqueous composition.

[0043] In one embodiment, the aqueous solvent may include water, distilled water, pure water, ultrapure water, or the like.

[0044] According to exemplary embodiments, the organic acid compound may include at least two oxygen-containing functional groups. The oxygen-containing functional groups may refer to terminal functional groups containing oxygen atoms.

[0045] For example, the oxygen-containing functional group may include a hydroxyl group (OH), a carboxyl group (COOH), an aldehyde group (CHO), and / or a carbonyl group (C=O).

[0046] The hydroxyl group of the above oxygen-containing functional group may be connected to a carbon atom that does not form a pi (π) bond with an oxygen atom. The carbonyl group of the above oxygen-containing functional group may not be connected to an -OH group and a hydrogen atom.

[0047] Organic acid compounds, which contain numerous oxygen-containing functional groups, can promote the movement of lithium ions between negative electrode active materials. For example, the oxygen-containing functional groups can shorten the movement path and increase the speed of lithium ions, thereby improving the ionic conductivity of negative electrodes for lithium secondary batteries. Consequently, the internal resistance of lithium secondary batteries can be reduced, leading to improved output characteristics.

[0048] In some embodiments, the organic acid compound may form a cross-linking bond with the binder within the negative electrode via the oxygen-containing functional group. For example, during the drying process of the negative electrode slurry, a chemical bond may be formed between the oxygen-containing functional group of the organic acid compound and the binder.

[0049] In one embodiment, when the cathode slurry is dried, a condensation reaction may occur between the organic acid compound and the binder. For example, a hydroxyl group or carboxyl group of an oxygen-containing functional group may form a covalent bond through dehydration with a carboxyl group or hydroxyl group contained in the binder. Accordingly, a cross-linked network in which the organic acid compound units and the binder units are linked to each other via oxygen atoms may be formed.

[0050] The formation of a cross-linking network between the binder and the organic acid compound can further improve the structural and mechanical stability of the negative electrode, and enhance the adhesion between the negative electrode active material layer and the negative electrode current collector. Therefore, volume expansion and swelling of the negative electrode due to repeated charge and discharge can be suppressed, and the detachment and peeling of the negative electrode active material layer can be prevented.

[0051] According to exemplary embodiments, in the molecular structure of the organic acid compound, the bond angle between oxygen-containing functional groups is 90 oThis may be ideal. The molecular structure of the organic acid compound may refer to a structural formula based on the plane of the organic acid compound. For example, the bond angle between the oxygen-containing functional groups may be calculated through the Lewis structure or skeletal formula of the organic acid compound.

[0052] The bond angle between oxygen-containing functional groups may refer to the internal angle formed by the bond lines of each of the oxygen-containing functional groups. For example, in the molecular structure of the organic acid compound, the internal angle between the bond lines may be 90. o Ideal, or 100 o It can be ideal. If the above bond lines are parallel to each other, the interior angle between the bond lines is 180. o am.

[0053] The bond line of the above oxygen-containing functional group may mean a straight line connecting the oxygen-containing functional group and the carbon atom bonded to the oxygen-containing functional group in the molecular structure (e.g., Lewis structure or skeletal structure) of the organic acid compound.

[0054] For example, in the compounds represented by the following chemical formulas 1 to 4, the internal angle between the bond lines of the oxygen-containing functional groups is 90 o That's all.

[0055] [Chemical Formula 1]

[0056]

[0057] [Chemical Formula 2]

[0058]

[0059] [Chemical Formula 3]

[0060]

[0061] [Chemical Formula 4]

[0062]

[0063] In Chemical Formula 1, the bond line a1 of the hydroxyl group is a straight line passing between the hydroxyl group (-OH) and the carbon atom connected to the hydroxyl group. The bond line a2 of the carboxyl group is a straight line passing between the carboxyl group (-COOH) and the carbon atom connected to the carboxyl group. In Chemical Formula 1, the internal angle θ between the bond lines of the oxygen-containing functional group is approximately 109.5 o am.

[0064] In chemical formula 2, the internal angle between bond lines a1 and a2 of the carboxyl group is approximately 180 o am.

[0065] In chemical formulas 3 and 4, the bond lines a1 and a2 of the carboxyl group are parallel to each other, and the internal angle formed by the bond lines is about 180. o am.

[0066] In one example, in the compounds represented by the following chemical formulae 5 to 7, the internal angle between the bond lines of the oxygen-containing functional groups is 90 o It is less than.

[0067] [Chemical Formula 5]

[0068]

[0069] [Chemical Formula 6]

[0070]

[0071] [Chemical Formula 7]

[0072]

[0073] In chemical formula 5, the internal angle θ between bond lines a1 and a2 of the carboxyl group is approximately 43.2 o In chemical formula 6, the internal angle θ between bond lines a1 and a2 of the carboxyl group and the internal angle θ' between bond lines a2 and a3 are each about 43.2 o In chemical formula 7, the internal angle θ between the bond line a1 of the hydroxyl group and the bond line a2 of the carboxyl group, and the internal angle θ' between the bond line a3 of the hydroxyl group and the bond line a4 of the carboxyl group are each about 43.2o am.

[0074] According to exemplary embodiments, the internal angles formed by the bond lines of the oxygen-containing functional groups included in the organic acid compound are all 90 o As a result, lithium ion conductivity can be further improved, and life characteristics and stability can be further improved.

[0075] For example, the internal angle between the bonds of oxygen-containing functional groups is 90 o If less than 0, the formation of cross-linking between the oxygen-containing functional groups of the organic acid compound and the binder may be hindered due to steric hindrance. In addition, the movement of lithium ions by the oxygen-containing functional groups may be reduced, which may deteriorate the output and life characteristics of the lithium secondary battery.

[0076] In some embodiments, the organic acid compound may include at least one acid compound selected from the group consisting of lactic acid, glycolic acid, succinic acid, fumaric acid, malonic acid, glutaric acid, adipic acid, pimelic acid, and oxalic acid. These may be used alone or in combination of two or more.

[0077] In one embodiment, the organic acid compound may have two or three oxygen-containing functional groups. Within the above range, the pH increase of the negative electrode slurry due to the high concentration of oxygen-containing functional groups can be suppressed, and the interaction between the binder and the organic acid compound and lithium ion conductivity can be further enhanced.

[0078] According to exemplary embodiments, the content of the organic acid compound may be greater than 0.01 wt% and less than 0.1 wt% of the total solid content of the aqueous negative electrode slurry. Within the above range, the viscosity and pH of the negative electrode slurry may be adjusted to an appropriate range, thereby improving the coatability of the negative electrode slurry, and enhancing the high-temperature stability and lifespan characteristics of the negative electrode.

[0079] In one embodiment, the total solid weight of the negative electrode slurry refers to the total weight of the components of the negative electrode slurry excluding the solvent. For example, the total solid weight may be the total weight of the negative electrode active material, the binder, and the organic acid compound. When the negative electrode slurry further includes a conductive material, etc., the total solid weight may be the total weight of the negative electrode active material, the binder, the organic acid compound, and the conductive material.

[0080] For example, when the content of the organic acid compound is 0.01 wt% or less, the oxygen-containing functional group exists in a low concentration, so the movement of lithium ions is not smooth, and there may be insufficient cross-linking points between the binder and the organic acid compound.

[0081] For example, when the content of the organic acid compound is 0.1 wt% or more, the adhesive strength between the negative electrode current collector and the negative electrode active material layer may be reduced due to the excessive amount of organic acid compound, and the high-temperature stability and life characteristics may be deteriorated.

[0082] In one embodiment, the content of the organic acid compound may be 0.02 wt% to 0.08 wt%, or 0.04 wt% to 0.08 wt%, of the total solid content of the aqueous cathode slurry. Within this range, the life characteristics, high-temperature stability, and electrode adhesion may be further improved.

[0083] According to exemplary embodiments, the binder may include a water-soluble thickening binder. The water-soluble thickening binder may include carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (Na-carboxymethyl cellulose), lithium carboxymethyl cellulose (Li-carboxymethyl cellulose), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyacrylamid (PAM), or a copolymer thereof.

[0084] In one embodiment, the copolymer may include at least two copolymers of polyvinyl alcohol, polyacrylic acid, and polyacrylamide. For example, the copolymer may include a copolymer of polyvinyl alcohol and polyacrylic acid (PVA-PAA copolymer) and / or a copolymer of polyacrylamide and polyacrylic acid (PAM-PAA copolymer).

[0085] By including the polymer compound described above as the binder, the dispersibility of the aqueous negative electrode slurry can be improved, and the coatability of the negative electrode slurry can be further enhanced. Furthermore, the polymer compound described above has high affinity and compatibility with organic acid compounds, allowing for the formation of a denser crosslinking network. Accordingly, the binding strength of the binder can be further improved, and the adhesive strength of the negative electrode active material layer can be further enhanced.

[0086] In some embodiments, the binder may further include an aqueous binder. The aqueous binder may include styrene-butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), acrylic rubber, hydroxyethyl cellulose, acrylate polymer, and the like.

[0087] In some embodiments, the content of the thickening binder in the total weight of the binder may be 20 wt% or more, 30 wt% or more, 50 wt% or more, or 70 wt% or more. In one embodiment, the content of the thickening binder in the total weight of the binder may be 95 wt% or less, 90 wt% or less, or 80 wt% or less.

[0088] Within the above range, the binder can be more uniformly dispersed within the negative electrode slurry, and a cross-linking network with the organic acid compound can be formed, thereby further enhancing the bonding strength. Accordingly, the internal resistance of the negative electrode can be reduced, and the life characteristics, thermal stability, and mechanical stability can be further improved.

[0089] In some embodiments, the content of the binder may be 0.5 wt% to 20 wt%, 1 wt% to 10 wt%, 2 wt% to 5 wt%, or 1 wt% to 4 wt% of the total solid content of the negative electrode slurry. Within this range, the internal resistance of the negative electrode may be lowered while the adhesive strength and structural stability of the negative electrode active material layer may be improved.

[0090] In some embodiments, the negative active material may include a silicon-containing material, a carbon-based active material, or a mixture thereof.

[0091] In some embodiments, the silicon-containing material is silicon (Si), silicon oxide (SiO X , 0 <x<2), 규소-금속합금 또는 규소-탄소 복합체(Si-C)를 포함할 수 있다. 이들은 단독으로 혹은 2 이상이 조합되어 포함될 수있다.

[0092] In one embodiment, SiO xmay include a lithium compound or a magnesium compound. For example, SiOx may be pretreated with lithium or magnesium to include lithium silicate or magnesium silicate, etc., on the interior and / or surface of the particle. The lithium silicate may include Li2SiO3, Li2Si2O5, Li4SiO4, Li4Si3O8, etc.

[0093] In some embodiments, the silicon-carbon composite may include silicon carbide (SiC) or silicon-carbon particles having a core-shell structure.

[0094] In some embodiments, the carbon-based active material may include crystalline carbon or amorphous carbon.

[0095] In one embodiment, the amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers (MPCF), and the like.

[0096] In one embodiment, the crystalline carbon may include graphitic carbon such as artificial graphite, natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and the like.

[0097] In one embodiment, the negative electrode active material may include a silicon-containing material. The silicon-containing material has a high energy density, which can increase the capacity of a lithium secondary battery. Furthermore, the organic acid compound can suppress the expansion of the negative electrode caused by the silicon-containing material, and the lithium ion conductivity can be supplemented, thereby improving both the output and lifespan characteristics of the lithium secondary battery.

[0098] In one embodiment, the negative active material may include a lithium alloy, silicon, tin, or the like. The lithium alloy may include lithium and aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, or the like.

[0099] In some embodiments, the content of the negative electrode active material may be 75 wt% to 99 wt%, 85 wt% to 98 wt%, or 95 wt% to 98 wt% of the total solid weight of the negative electrode slurry. Within this range, the energy density of the negative electrode may be improved, and the output and capacity of the lithium secondary battery may be further improved.

[0100] In some embodiments, the cathode slurry may further include a conductive material. The conductive material may facilitate electron transport. For example, the conductive material may include a carbon-based conductive material, such as graphite, carbon black, graphene, or carbon nanotubes, and / or a metal-based conductive material, such as tin, tin oxide, titanium oxide, LaSrCoO3, or LaSrMnO3.

[0101] In one embodiment, the content of the conductive material may be 0.5 wt% to 5 wt%, or 1 wt% to 3 wt%, of the total solid weight of the negative electrode slurry.

[0102] In some embodiments, the pH of the cathode slurry may be 8 or less. Accordingly, the viscosity of the cathode slurry can be adjusted to an appropriate range, dispersibility can be improved, and the generation of byproducts such as hydrogen gas can be suppressed, thereby improving the processability and stability of the cathode slurry.

[0103] In one embodiment, the pH of the negative electrode slurry may be 6 to 8. Within this range, side reactions of the negative electrode active material and generation of hydrogen gas can be suppressed, and the output, capacity, and life characteristics of the lithium secondary battery can be improved.

[0104] In one embodiment, the pH of the cathode slurry can be measured using a pH meter. The pH meter may be a CAS Benchtop pH tester PM-3 or the like.

[0105] The negative electrode for a lithium secondary battery according to embodiments of the present disclosure (hereinafter, abbreviated as negative electrode) can be manufactured using the above-described negative electrode slurry.

[0106] For example, the negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector. The negative electrode active material layer may be formed on both surfaces (e.g., the upper surface and the lower surface) of the negative electrode current collector.

[0107] The negative electrode active material layer can be formed by applying, drying, and / or rolling the above-described negative electrode slurry onto at least one surface of the negative electrode current collector. For example, the negative electrode active material layer can include a negative electrode active material, a binder, and the organic acid compound.

[0108] The negative electrode current collector may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof. For example, the negative electrode current collector may include copper or a copper alloy.

[0109] According to exemplary embodiments, the content of the organic acid compound may be greater than 0.01 wt% and less than 0.1 wt%, 0.02 wt% to 0.08 wt%, or 0.04 wt% to 0.08 wt% of the total weight of the negative electrode active material layer.

[0110] In some embodiments, the content of the negative active material may be 75 wt% to 99 wt%, 85 wt% to 98 wt%, or 95 wt% to 98 wt% of the total weight of the negative active material layer.

[0111] In some embodiments, the content of the binder may be 0.5 wt% to 20 wt%, 1 wt% to 10 wt%, 2 wt% to 5 wt%, or 1 wt% to 4 wt% of the total weight of the negative electrode active material layer.

[0112] In one embodiment, the negative electrode active material layer may further include a conductive material. In one embodiment, the content of the conductive material may be 0.5 wt% to 5 wt%, or 1 wt% to 3 wt%, of the total weight of the negative electrode active material layer.

[0113] In some embodiments, the binder and the organic acid compound within the negative electrode active material layer may be cross-linked with each other. For example, the oxygen-containing functional groups of the organic acid compound may act as cross-linking sites for the binder, thereby linking the binders to each other. Accordingly, a dense cross-linking network may be formed within the negative electrode active material layer, thereby improving the structural / mechanical stability of the negative electrode active material layer and increasing the adhesion between the negative electrode active material layer and the negative electrode current collector.

[0114] In some embodiments, the adhesive strength between the negative electrode active material layer and the negative electrode current collector may be 0.5 N / 18 mm or greater. Since the negative electrode active material layer has high adhesive strength to the negative electrode current collector, volume expansion of the negative electrode and detachment or peeling of the negative electrode active material layer can be prevented. In addition, electron movement between the negative electrode current collector and the negative electrode active material layer can be further promoted, thereby reducing the internal resistance of the negative electrode.

[0115] In one embodiment, the adhesion between the negative active material layer and the negative current collector can be measured using an adhesion measuring device for the electrode substrate. Examples of the adhesion measuring device include the DS2-50N from IMADA.

[0116] In one embodiment, the adhesive strength between the negative electrode active material layer and the negative electrode current collector may be 0.5 N / 18 mm to 0.6 N / 18 mm, or 0.51 N / 18 mm to 0.58 N / 18 mm.

[0117] A lithium secondary battery according to embodiments of the present disclosure may include the above-described negative electrode and a positive electrode opposite to the negative electrode.

[0118] FIG. 1 and FIG. 2 are schematic plan views and cross-sectional views, respectively, showing lithium secondary batteries according to exemplary embodiments.

[0119] Referring to FIGS. 1 and 2, a lithium secondary battery may include a positive electrode (100) and a negative electrode (130) opposite to the positive electrode (100).

[0120] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) formed on at least one surface of the negative electrode current collector (125).

[0121] The positive electrode (100) may include a positive electrode current collector (105) and a positive electrode active material layer (110) formed by coating a positive electrode active material on at least one surface of the positive electrode current collector (105).

[0122] For example, a positive electrode slurry can be prepared by mixing and stirring a positive electrode active material with a positive electrode conductive material and / or a positive electrode binder in a solvent. The positive electrode slurry can be applied onto a positive electrode current collector (105), dried, and pressed to form a positive electrode (100).

[0123] The positive electrode current collector (105) may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector (105) may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver.

[0124] As an example of the positive electrode active material, it may include one or more compounds selected from lithium iron phosphate compounds, lithium cobalt oxides, lithium manganese oxides, lithium nickel oxides, or lithium composite oxides. For example, the positive electrode active material may include layered compounds such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); LiV3O8, LiFe3O4, V2O 5　 It may include vanadium oxides such as Cu2VO7, lithium iron phosphate oxides such as LiFePO4, etc.

[0125] In one embodiment, the positive electrode active material may include a compound represented by chemical formula 8.

[0126] [Chemical Formula 8]

[0127] Li a Ni b M 1-b O2

[0128] In chemical formula 8, 0.95≤a≤1.10, b≥0.5, and M may be at least one element among Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Ba, and Zr.

[0129] In one embodiment, the lithium transition metal oxide comprises nickel (Ni) and may further comprise at least one of cobalt (Co) and manganese (Mn). For example, the lithium transition metal oxide may comprise a nickel-cobalt-manganese (NCM) lithium oxide.

[0130] Nickel (Ni) can be used as a metal associated with the capacity of lithium secondary batteries. While higher nickel content can improve the capacity and output of lithium secondary batteries, excessive nickel content can shorten the battery's lifespan and compromise mechanical and electrical stability.

[0131] In one embodiment, the conductivity or resistance of a lithium secondary battery may be improved by cobalt (Co). In one embodiment, the mechanical and electrical stability of a lithium secondary battery may be improved by manganese (Mn).

[0132] The chemical structure represented by Chemical Formula 8 represents the bonding relationship contained within the lattice structure or crystal structure of a lithium transition metal oxide and does not exclude other additional elements. For example, M may serve as the main active element of a lithium transition metal oxide. Chemical Formula 8 is provided to express the bonding relationship of the main active element and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0133] In one embodiment, auxiliary elements may be further included in addition to the main active element to enhance the chemical stability of the crystal structure. The auxiliary elements may be incorporated into the crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 8.

[0134] The above positive electrode binder may include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, nitrile butadiene rubber, etc.

[0135] The above-mentioned positive electrode conductive material may include a carbon-based conductive material such as graphite, carbon black, graphene, carbon nanotubes, etc., and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0136] In some embodiments, a separator (140) may be interposed between the positive electrode (100) and the negative electrode (130). The separator (140) may include a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or the like. The separator (140) may also include a nonwoven fabric formed of high-melting-point glass fibers, polyethylene terephthalate fibers, or the like.

[0137] According to exemplary embodiments, an electrode cell is defined by an anode (100), a cathode (130), and a separator (140), and a plurality of the electrode cells may be repeatedly arranged to form an electrode assembly (150). In some embodiments, the electrode assembly (150) may be of a winding type, a stacking type, a z-folding type, or a stack-folding type.

[0138] A lithium secondary battery may be defined by housing an electrode assembly (150) together with the electrolyte described above within a case (160). For example, the electrolyte described above may impregnate the electrode assembly (150).

[0139] As illustrated in FIG. 1, electrode tabs (positive electrode tabs and negative electrode tabs) may protrude from the positive electrode collector (105) and negative electrode collector (125) belonging to each electrode cell and extend to one side of the case (160). The electrode tabs may be fused together with the one side of the case (160) to form electrode leads (positive electrode leads (107) and negative electrode leads (127)) that extend or are exposed to the outside of the case (160).

[0140] The above lithium secondary battery can be manufactured in a cylindrical, square, pouch or coin shape using, for example, a can.

[0141]

[0142] Hereinafter, embodiments of the present disclosure will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the examples are possible within the scope and technical idea of ​​the present disclosure, and it is also natural that such changes and modifications fall within the scope of the appended claims.

[0143]

[0144] Examples and Comparative Examples

[0145] (1) Preparation of cathode slurry

[0146] Graphite (86.8-x) wt% and silicon oxide (SiOx, 0) as negative active materials <x<2) 10중량%, 도전재로 탄소나노튜브(CNT) 0.5중량%, 바인더 2.7중량% 및 유기산 화합물 x중량%를 물에 첨가하고 혼합하여 음극 슬러리를 제조하였다. 바인더 및 유기산 화합물은 하기 표 1의 종류 및 / 또는 함량(중량%)으로 첨가되었다.

[0147] The number of oxygen-containing functional groups (number of functional groups) of organic acid compounds and the bond angles between oxygen-containing functional groups are shown in Table 1 below. The bond angle between oxygen-containing functional groups is the smallest value among the internal angles formed by the bond lines of oxygen-containing functional groups.

[0148]

[0149] Binder Organic Acid Compound Type Type Functional Group Number Bond Angle Content (x wt%) Example 1 A1B 12 1800.04 Example 2 A1B 22 1800.04 Example 3 A1B 32 109.50.02 Example 4 A1B 32 109.50.04 Example 5 A1B 32 109.50.08 Example 6 A2B 32 109.50.04 Example 7 A3B 32 109.50.04 Example 8 A1B 42 109.50.04 Example 9 A1B 32 109.50.015 Example 10 A1B 32 109.50.09 Example 11 A1B 32 109.50.04 Example 12 A4B 32 109.50.04 Example 13A5B32109.50.04Comparative Example 1A1----Comparative Example 2A1B32109.50.01Comparative Example 3A1B32109.50.1Comparative Example 4A1B51-0.04Comparative Example 5A1B6443.20.04Comparative Example 6A1B7443.20.04Comparative Example 7A1B8243.20.04Comparative Example 8A2----Comparative Example 9A3----

[0150] The specific compounds listed in Table 1 are as follows.

[0151] A1: Sodium carboxymethyl cellulose (CMC) and SBR (CMC:SBR = 1.2:1.5 weight ratio)

[0152] A2: PAA-PVA copolymer (PVA 40 wt%, PAA 60 wt%) and SBR (PAA-PVA:SBR = 2.0:0.7 weight ratio)

[0153] A3: PAA-PAM copolymer (PAM 40 wt%, PAA 60 wt%) and SBR (PAA-PAM:SBR = 2.0:0.7 weight ratio)

[0154] A4: PAA-PVA copolymer (PVA 40 wt%, PAA 60 wt%) and SBR (PAA-PVA: SBR = 2.2:0.5 weight ratio)

[0155] A5: PAA-PAM copolymer (PAM 40 wt%, PAA 60 wt%) and SBR (PAA-PAM: SBR = 2.2:0.5 weight ratio)

[0156] B1: fumaric acid

[0157] B2: Oxalic acid

[0158] B3: Lactic acid

[0159] B4: succinic acid

[0160] B5: Acetic acid

[0161] B6: citric acid

[0162] B7: Tartanic acid

[0163] B8: maleic acid

[0164]

[0165] (2) Manufacturing of lithium secondary batteries

[0166] Using the above negative electrode slurry, a negative electrode active material layer was formed on a negative electrode current collector. Specifically, the negative electrode slurry was uniformly coated on an 8 μm thick copper foil (negative electrode current collector), dried, and pressed to manufacture the negative electrode.

[0167] LiNi as positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, carbon nanotubes (CNTs) as a conductive agent, and PVdF as a binder were mixed in a weight ratio of 97.3:1.5:1.2 to prepare a cathode slurry. The cathode slurry was uniformly applied to a 10 μm thick aluminum foil, dried, and rolled to prepare a cathode.

[0168] The positive and negative electrodes were each cut to a predetermined size and laminated, and a separator (polyethylene, 14 μm thick) was interposed between the positive and negative electrodes to manufacture an electrode assembly.

[0169] The above electrode assembly was placed in an outer case and an electrolyte was injected to manufacture a lithium secondary battery. The electrolyte was prepared by dissolving 5 wt% of FEC additive and 1 M LiPF6 in an EC / EMC (30:70 v / v) mixed solvent.

[0170]

[0171] Experimental example

[0172] (1) pH measurement of cathode slurry

[0173] The pH of the cathode slurry manufactured according to the above-described examples and comparative examples was measured using a pH meter (CAS Benchtop pH tester PM-3).

[0174]

[0175] (2) Evaluation of negative electrode adhesion

[0176] The adhesion between the negative electrode current collector and the negative electrode active material layer was measured using an adhesion measuring device (DS2-50N from IMADA).

[0177] Specifically, double-sided tape was attached to an adhesive strength measurement jig, and the current collector side of the manufactured negative electrode was positioned on the tape, and the tape was attached by reciprocating the roller 10 times. After that, the tape was cut to a width of 18 mm and attached to the center of the measurement jig with the tape side facing downward. Thereafter, the adhesive strength of the negative electrode active material layer was measured while moving the adhesive strength measuring device at a speed of 300 rpm.

[0178]

[0179] (3) Cathode swelling evaluation

[0180] After measuring the thickness (T0) of the rolled negative electrode, a lithium secondary battery manufactured using the negative electrode was charged to SOC100, and the battery was disassembled to measure the thickness (T1) of the obtained negative electrode. The increased thickness (T1-T0) of the fully charged negative electrode compared to the rolled negative electrode was converted into a percentage (%) of the thickness (T0) of the rolled negative electrode to evaluate the swelling (%).

[0181] Swelling(%) = ((T1-T0) / T0)X100

[0182]

[0183] (4) Life characteristics evaluation

[0184] A lithium secondary battery was charged (CC-CV 0.3 C 4.2 V 0.05 C CUT-OFF) and discharged (CC 0.5 C 2.5 V CUT-OFF) three times in a 25°C chamber, and the third discharge capacity was set as the initial discharge capacity. After that, 500 cycles were performed with charge and discharge as one cycle, and the discharge capacity at the 500th cycle was measured.

[0185] The life characteristics were evaluated by converting the value obtained by dividing the initial discharge capacity by the measured discharge capacity at 500 cycles into a percentage (%).

[0186]

[0187] (5) High temperature stability evaluation

[0188] Lithium secondary batteries were charged (0.3C) to SOC98 of the initial discharge capacity and stored in a 60°C oven for 20 weeks. The time required for the pouch to burst due to gas generated inside the lithium secondary battery was then measured.

[0189]

[0190] The evaluation results are shown in Table 2 below.

[0191] Slurry pH Adhesion (N / 18mm) Swelling (%) Lifetime characteristics (%) High temperature stability (weeks) Example 1 7.20.56 30.09 0.927 Example 2 7.20.55 29.99 0.727 Example 3 7.20.56 30.88 9.928 Example 4 7.20.56 30.29 0.528 Example 5 7.10.51 30.19 0.627 Example 6 70.51 27.89 3.327 Example 7 7.10.46 29.49 0.326 Example 8 7.20.55 30.49 0.127 Example 9 7.40.55 318 7.228 Example 10 70.46 308 5.927 Example 117.10.5531.180.827 Example 127.20.5530.984.825 Example 137.20.4229.284.325Comparative Example 17.40.5731.684.228Comparative Example 27.30.5631.584.428Comparative Example 37.10.4130.080.824Comparative Example 47.40.5531.784.027Comparative Example 57.10.5231.484.422Comparative Example 67.10.5331.684.222Comparative Example 77.20.5531.085.528Comparative Example 87.10.5230.988.726Comparative Example 97.20.4431.387.326

[0192] Referring to Tables 1 and 2, the negative electrodes for lithium secondary batteries manufactured using the negative electrode slurries of the examples exhibited high adhesive strength and low swelling characteristics. Furthermore, the lithium secondary batteries of the examples exhibited high cycle life characteristics even after repeated charge and discharge, and improved high-temperature stability.

[0193] However, in the case of Comparative Examples 1, 8, and 9 in which the negative electrode slurry did not contain an organic acid compound, the swelling characteristics and life characteristics of the negative electrode deteriorated. In the case of Comparative Example 2 in which the organic acid compound was contained at 0.01 wt% of the total solid content, the swelling characteristics and life characteristics of the negative electrode deteriorated. In the case of Comparative Example 3 in which the organic acid compound was contained at 0.1 wt% of the total solid content, the negative electrode active material layer had low adhesive strength, and the life characteristics and high-temperature stability were significantly deteriorated.

[0194] In Comparative Examples 4 to 7, the cathode slurry contained an organic acid compound having one oxygen-containing functional group or a low bond angle, and the adhesive strength, swelling characteristics, life characteristics, and high-temperature stability were all reduced.

Claims

1. Negative active material; binder; and Comprising an organic acid compound having at least two oxygen-containing functional groups, In the molecular structure of the above organic acid compound, the bond angle between the oxygen-containing functional groups is 90 o That's all, An aqueous cathode slurry, wherein the content of the organic acid compound is greater than 0.01 wt% and less than 0.1 wt% of the total solid weight of the aqueous cathode slurry.

2. In claim 1, the binder is an aqueous negative electrode slurry comprising carboxymethyl cellulose, sodium carboxymethyl cellulose (Na-carboxymethyl cellulose), lithium carboxymethyl cellulose (Li-carboxymethyl cellulose), polyvinyl alcohol, polyacrylic acid, polyacrylamide, or a copolymer thereof.

3. In claim 1, the binder is an aqueous negative electrode slurry comprising polyvinyl alcohol, polyacrylic acid, polyacrylamide, or a copolymer thereof.

4. An aqueous negative electrode slurry according to any one of claims 1 to 3, wherein the negative electrode active material comprises a silicon-containing material.

5. An aqueous cathode slurry according to any one of claims 1 to 4, wherein the oxygen-containing functional group comprises an aldehyde group, a carboxyl group, or a hydroxyl group connected to a carbon atom that does not form a pi (π) bond with an oxygen atom.

6. An aqueous cathode slurry according to any one of claims 1 to 5, wherein the bond angle between the oxygen-containing functional groups is an internal angle between bond lines connecting the oxygen-containing functional group and the carbon atom bonded to the oxygen-containing functional group in the molecular structure of the organic acid compound.

7. An aqueous cathode slurry according to any one of claims 1 to 6, wherein the organic acid compound comprises at least one acid compound selected from the group consisting of lactic acid, glycolic acid, succinic acid, fumaric acid, malonic acid, glutaric acid, adipic acid, pimelic acid, and oxalic acid.

8. An aqueous cathode slurry according to any one of claims 1 to 6, wherein the organic acid compound has two or three oxygen-containing functional groups.

9. An aqueous cathode slurry according to any one of claims 1 to 8, wherein the content of the organic acid compound is 0.02 wt% to 0.08 wt% of the total solid content of the aqueous cathode slurry.

10. An aqueous cathode slurry according to any one of claims 1 to 9, further comprising an aqueous solvent.

11. An aqueous cathode slurry according to any one of claims 1 to 10, wherein the pH of the aqueous cathode slurry is 8 or less.

12. A negative electrode active material layer comprising a negative electrode active material, a binder, and an organic acid compound having at least two oxygen-containing functional groups, In the molecular structure of the above organic acid compound, the bond angle between the oxygen-containing functional groups is 90 o That's all, A negative electrode for a lithium secondary battery, wherein the content of the organic acid compound is more than 0.01 wt% and less than 0.1 wt% of the total weight of the negative electrode active material layer.

13. A negative electrode for a lithium secondary battery, wherein the organic acid compound is cross-linked with the binder in claim 12.

14. In claim 12 or 13, further comprising a negative electrode current collector, A negative electrode for a lithium secondary battery, wherein the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector.

15. A negative electrode for a lithium secondary battery according to claim 14, wherein the adhesive strength between the negative electrode active material layer and the negative electrode current collector is 0.5 N / 18 mm or more.

16. A negative electrode for a lithium secondary battery according to any one of claims 12 to 15; and A lithium secondary battery comprising a cathode opposite to the cathode for the lithium secondary battery.

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