Electrode for rechargeable lithium battery and rechargeable lithium battery including the same

Abstract

An electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same are provided. The electrode comprises a current collector; and an electrode active material layer on the current collector and including an active material, a first conductive material, and a binder, in which the first conductive material includes: a core including graphene, graphene oxide, reduced graphene oxide, or a combination thereof; and a coating layer on a surface of the core and including alumina nanoparticles.

Description

Technical Field

[0001] Disclosed are an electrode for a rechargeable lithium battery and a rechargeable lithium battery including the electrode. Background Art

[0002] With the industrial development of medium to large-sized rechargeable batteries for electric vehicles, interest in rechargeable lithium batteries having high energy density is emerging.

[0003] As a strategy to improve the energy density of rechargeable lithium batteries, thick film electrodes can be applied. However, if a wet process is applied to manufacture the electrode, its microstructure deteriorates according to the binder migration in the subsequent drying process, which may limit or reduce the thickening of the electrode. In this regard, a method of manufacturing an electrode using a dry process has been proposed, which has the characteristics of low cost and environmental protection in addition to easy thickening of the electrode.

[0004] However, the dry process mainly uses polytetrafluoroethylene (PTFE) having high electrical and ionic resistance as an electrode binder. Therefore, compared with electrodes manufactured by the wet process, electrodes manufactured by the dry process have the disadvantage of high resistance.

[0005] After the electrode is manufactured by a dry process, the properties of the electrode film (e.g., tensile strength, ductility, etc.) are ensured by a subsequent process of forming the electrode into a film. Therefore, it would be beneficial to introduce a conductive material (e.g., an electrically conductive material and / or an ion conductive material) that can improve the properties of the electrode film and reduce the resistance of the electrode film therein, but little research has been done on this. Summary of the invention

[0006] Some embodiments of the present disclosure provide an electrode for a rechargeable lithium battery that includes a conductive material (e.g., an electrically conductive material and / or an ion conductive material) that can improve the physical properties of an electrode film manufactured by a dry process and reduce resistance (e.g., electrical resistance and / or ionic resistance).

[0007] Some embodiments provide a rechargeable lithium battery including the electrode.

[0008] Some embodiments provide an electrode for a rechargeable lithium battery, the electrode comprising: a current collector; and an electrode active material layer, on the current collector and comprising an active material, a first conductive material (e.g., a first electrically conductive material and / or an ion conductive material), and a binder, wherein the first conductive material comprises: a core, comprising graphene, graphene oxide, reduced graphene oxide, or a combination thereof; and a coating layer, on the surface of the core, and comprising aluminum oxide nanoparticles.

[0009] The electrode according to some embodiments may improve physical properties of the electrode even if manufactured by a dry process and may exhibit low resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The drawings, together with the specification, illustrate embodiments of the presently disclosed subject matter, and, together with the description, serve to explain principles of the embodiments of the presently disclosed subject matter.

[0011] Figure 1 is a schematic perspective view illustrating a rechargeable lithium battery according to some embodiments.

[0012] Figure 2 is an image of the surface of the first conductive material observed using a scanning electron microscope (SEM) apparatus in Examples.

[0013] Figure 3 is an image showing energy dispersive X-ray spectroscopy (EDS) mapping analysis of the surface of the first conductive material in the example.

[0014] Figure 4 is a graph showing the results of measuring the tensile strength and elongation of an electrode in a vertical direction in some embodiments.

[0015] Figure 5 is a graph showing the results of measuring the tensile strength and elongation of an electrode in a horizontal direction in some embodiments.

[0016] Figure 6 is a graph showing charge / discharge behaviors of a rechargeable lithium battery cell according to an example measured at each C rate of 0.1C and 1C.

[0017] Figure 7 is a graph showing charge / discharge behaviors of a rechargeable lithium battery cell according to an example measured at a C-rate of 2C.

[0018] Figure 8 2 is a diagram showing R of a rechargeable lithium battery cell according to an example ion Graph of the curve.

[0019] Fig. 9 2 is a diagram showing R of a rechargeable lithium battery cell according to an example ct Graph of the curve. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present disclosure will be described in more detail. However, these embodiments are examples, the present disclosure is not limited thereto, and the present disclosure is defined by the scope of the appended claims and their equivalents.

[0021] As used herein, if no specific definition is provided otherwise, it will be understood that if an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present.

[0022] As used herein, if no specific definition is otherwise provided, the singular may also include the plural. In an embodiment, "A or B" may mean "including A, including B, or including A and B", unless otherwise specified.

[0023] As used herein, "combinations thereof" may refer to mixtures, stacks, composites, copolymers, alloys, blends, and reaction products of the components.

[0024] As used herein, if no definition is otherwise provided, the particle size may be an average particle size. The average particle size may be an average particle size (D 50 ). Average particle size (D 50 ) can be measured by any suitable method commonly used in the art (e.g., by a particle size analyzer, a transmission electron microscope and / or a scanning electron microscope). In an embodiment, a dynamic light scattering measurement device can be used to perform data analysis, and the number of particles can be counted for each particle size range. Thus, the average particle size (D) can be easily obtained by calculation. 50 ) value. A laser diffraction method may be used. If the measurement is performed by laser diffraction, for example, the particles to be measured are dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measuring device (e.g., MT3000 available from Microtrac Corporation), and after irradiation with ultrasonic waves of about 28 kHz at an output of 60 W, the average particle size (D ) based on 50% of the particle size distribution in the measuring device can be calculated. 50 ).

[0025] electrode

[0026] Some embodiments provide an electrode for a rechargeable lithium battery, the electrode comprising: a current collector; and an electrode active material layer, on the current collector and comprising an active material, a first conductive material (e.g., a first electrically conductive material and / or an ion conductive material) and a binder, wherein the first conductive material comprises a core and a coating layer, the core comprising graphene, graphene oxide, reduced graphene oxide or a combination thereof, and the coating layer is on the surface of the core and comprises aluminum oxide nanoparticles.

[0027] Electrode thickening to increase conductive and ion transport paths in the electrode to ensure high energy density increases the overall resistance (eg, electrical resistance and / or ionic resistance) in the electrode and degrades the electrochemical properties (eg, tensile strength, ductility, etc.) of the electrode film.

[0028] In this regard, some methods of improving the resistance of electrodes manufactured in a wet process have been reported, but few methods of improving the resistance (eg, electrical resistance and / or ionic resistance) of electrodes manufactured in a dry process have been reported.

[0029] Some embodiments introduce a first conductive material (e.g., a first electrically conductive material and / or an ion conductive material) that can improve the properties of the electrode film and reduce the resistance (e.g., electrical resistance and / or ionic resistance) therein while using a dry process to manufacture the electrode.

[0030] The first conductive material includes: a core including graphene, graphene oxide, reduced graphene oxide, or a combination thereof; and a coating layer on a surface of the core and including aluminum oxide nanoparticles.

[0031] Graphene, graphene oxide, and reduced graphene oxide constituting the first conductive material are materials having low resistance, high conductivity, and excellent properties (tensile strength, elongation, etc.). Therefore, a dry electrode comprising graphene, graphene oxide, reduced graphene oxide, or a combination thereof as a core of the first conductive material can offset the high resistance of the binder and ensure high conductivity and excellent properties.

[0032] In an embodiment, graphene, graphene oxide, and reduced graphene oxide are materials having a two-dimensional (2D) nanoplate shape, which have a specific surface area larger than that of a material having a 0D shape, such as carbon black, etc. Therefore, the first conductive material into which graphene, graphene oxide, reduced graphene oxide, or a combination thereof is introduced into the core may exist discontinuously in the form of surrounding the dry binder but not blocking the surface of the active material, thereby maintaining the pore structure inside the electrode.

[0033] In an embodiment, the aluminum oxide nanoparticles may control the surface properties of the core to form a microporous structure inside the electrode, and are lithiophilic to improve ionic conductivity around the core.

[0034] In some embodiments, the first conductive material is introduced into the electrode, which can show improved properties and low resistance (e.g., low electrical resistance and / or ionic resistance) compared to the electrode using only carbon black as the conductive material, even when manufactured in a dry process.

[0035] Hereinafter, electrodes of some embodiments will be described in more detail.

[0036] The coating layer may be included in an amount of about 1 part by weight to about 100 parts by weight, about 5 parts by weight to about 80 parts by weight, or about 10 parts by weight to about 50 parts by weight, based on 100 parts by weight of the core.

[0037] Within the above range, as the content of the coating layer decreases, the resistivity (eg, electrical resistivity and / or ion resistivity) of the surface of the positive electrode active material layer decreases, and the charge / discharge behavior may be improved.

[0038] The coating layer may be in the form of dots. In an embodiment, compared with a uniform (or substantially uniform) coating form, it may be beneficial to form a fine pore structure within the electrode.

[0039] The aluminum oxide nanoparticles may have a D of about 10 nm to about 100 nm, about 20 nm to about 90 nm, or about 30 to about 60 nm. 50 Particle size.

[0040] Within the above range, the aluminum oxide nanoparticles may be effectively coated on the surface of the core.

[0041] The electrode active material layer may include a first conductive material as the only conductive material (e.g., the only electrically conductive material and / or ion conductive material or additive in the electrode active material layer), or may further include a second conductive material (e.g., a second electrically conductive material and / or ion conductive material). The second conductive material may include carbon black.

[0042] In embodiments, a weight ratio of the first conductive material to the second conductive material may be about 1:9 to about 9:1, about 1:7 to about 7:1, about 1:5 to about 5:1, or about 1:3 to about 3:1.

[0043] Since carbon black is a 0D-like material, if combined with a first conductive material having a 2D nanoplate shape, it may be suitable or expected to form or provide a fine pore structure within an electrode.

[0044] The binder may be a dry binder.

[0045] The dry binder may be a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0046] For example, the binder may be polytetrafluoroethylene.

[0047] In an embodiment, the electrode may be a positive electrode, and the active material may be a positive electrode active material.

[0048] Positive electrode active material

[0049] The positive electrode active material may be a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). For example, one or more types (or species) of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0050] The composite oxide may be a lithium transition metal composite oxide, and examples thereof may include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free lithium nickel manganese-based oxides, or combinations thereof.

[0051] For example, the positive electrode active material can be a high nickel-based positive electrode active material having a nickel content of metals other than lithium greater than or equal to about 80 mol% based on 100 mol% of the lithium transition metal composite oxide. Based on 100 mol% of the metals other than lithium in the lithium transition metal composite oxide, the nickel content in the high nickel-based positive electrode active material can be greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%. The high nickel-based positive electrode active material can achieve high capacity and can be applied to high capacity, high density rechargeable lithium batteries.

[0052] As an example, a compound represented by any one of the following chemical formulae may be used. a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b- c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1d G e O 2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NeG b O 2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O 2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O 2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 2 G b O 4 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO 4 (0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe 2 (PO 4 ) 3 (0≤f≤2); and Li a FePO 4 (0.90≤a≤1.8).

[0053] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; and L 1 It is Mn, Al or a combination thereof.

[0054] Positive electrode

[0055] The positive electrode for a rechargeable lithium battery may include a current collector and a positive electrode active material layer on the current collector. The positive electrode active material layer includes a positive electrode active material and may also include a binder and / or a conductive material (eg, an electrically conductive material and / or an ion conductive material).

[0056] The content of the positive electrode active material may be about 90 wt % to about 99.5 wt % based on 100 wt % of the positive electrode active material layer.

[0057] In some embodiments, the positive electrode active material layer may further include a binder and a conductive material (e.g., an electrically conductive material and / or an ion conductive material). At this time, the contents of the binder and the conductive material may be about 0.5 wt % to about 5 wt % based on 100 wt % of the positive electrode active material layer.

[0058] The binder is used to make the positive electrode active material particles adhere well to each other, and also to attach the positive electrode active material well to the current collector. Examples of the binder can be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth) acrylated styrene-butadiene rubber, epoxy resin, (meth) acrylic resin, polyester resin, nylon and combinations thereof, but are not limited thereto.

[0059] Conductive materials can be used to impart conductivity (e.g., electrical conductivity) to electrodes, and any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in rechargeable lithium batteries) and conducts electrons can be used in the battery. Examples of conductive materials may include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, carbon nanotubes, and graphene; metal-based materials in the form of metal powders and / or metal fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers (e.g., electrically conductive polymers) such as polyphenylene derivatives; and / or mixtures thereof.

[0060] The current collector may include Al, but is not limited thereto.

[0061] Rechargeable lithium battery

[0062] A rechargeable lithium battery according to some embodiments may be classified into a cylindrical, prismatic, pouch or coin type battery, etc., according to its shape. Figure 1 is a schematic perspective view showing a rechargeable lithium battery according to some embodiments. Figure 1 , the rechargeable lithium battery 100 may include an electrode assembly and a case 50, the electrode assembly including a separator 30 between a positive electrode 10 and a negative electrode 20, and the electrode assembly is accommodated in the case 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte. Figure 1 As shown in , the rechargeable lithium battery 100 may include a sealing member 60 for sealing the case 50 .

[0063] A rechargeable lithium battery according to some embodiments may include the above-described positive electrode.

[0064] In the following, descriptions overlapping with the above will not be repeated, and rechargeable lithium batteries according to some embodiments will be described in more detail.

[0065] Negative electrode active material

[0066] The negative electrode active material may be a material that can reversibly intercalate / deintercalate lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, and / or a transition metal oxide.

[0067] The material that can reversibly intercalate / deintercalate lithium ions may include carbon-based negative electrode active materials, such as crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be graphite, such as natural graphite and / or artificial graphite in irregular shapes, flakes, lamellae, spheres, and / or fibrous forms. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0068] The lithium metal alloy may include lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0069] The material capable of doping / dedoping lithium may be a Si-based negative electrode active material and / or a Sn-based negative electrode active material. The Si-based negative electrode active material may include silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), a Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, or a combination thereof, such as Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and a combination thereof) or a combination of them. The Sn-based negative electrode active material may include Sn, SnO 2 , a Sn alloy, or a combination thereof.

[0070] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D 50) can be, for example, from about 0.5 μm to about 20 μm. According to some embodiments, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) in which silicon primary particles are aggregated and an amorphous carbon coating layer (shell) on the surface of the secondary particles. Amorphous carbon can also be present between the silicon primary particles. For example, the silicon primary particles can be coated with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0071] The silicon-carbon composite can also include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer on the surface of the core. The crystalline carbon can be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon can include soft carbon and / or hard carbon, mesophase pitch carbonized products, calcined coke, etc.

[0072] If the silicon-carbon composite includes silicon and amorphous carbon, then based on 100 wt% of the silicon-carbon composite, the content of silicon can be from about 10 wt% to about 50 wt%, and the content of amorphous carbon can be from about 50 wt% to about 90 wt%. In an embodiment, if the composite includes silicon, amorphous carbon, and crystalline carbon, then based on 100 wt% of the silicon-carbon composite, the content of silicon can be from about 10 wt% to about 50 wt%, the content of crystalline carbon can be from about 10 wt% to about 70 wt%, and the content of amorphous carbon can be from about 20 wt% to about 40 wt%.

[0073] In an embodiment, the thickness of the amorphous carbon coating layer can be from about 5 nm to about 100 nm. The average particle size (D 50 ) of the silicon particles (silicon primary particles) can be from about 10 nm to about 1 μm, or from about 10 nm to about 200 nm. The silicon particles can exist alone as silicon, in the form of a silicon alloy, and / or in an oxidized form. The oxidized form of silicon can be represented by SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation can be from about 99:1 to about 33:67. As used herein, if no other definition is provided, the average particle size (D 50 ) represents the average diameter of the particles with a cumulative volume of about 50% by volume in the particle size distribution.

[0074] Si-based negative electrode active materials and / or Sn-based negative electrode active materials can be used in combination with carbon-based negative electrode active materials. If the Si-based negative electrode active materials and / or Sn-based negative electrode active materials are mixed and used with the carbon-based negative electrode active materials, the mixing ratio can be a weight ratio of from about 1:99 to about 90:10.

[0075] Negative electrode

[0076] The negative electrode for a rechargeable lithium battery includes a current collector and a negative electrode active material layer on the current collector. The negative electrode active material layer includes a negative electrode active material and may also include a binder and / or a conductive material (eg, an electrically conductive material and / or an ion conductive material).

[0077] Based on 100wt% of the negative electrode active material layer, the content of the negative electrode active material may be about 90wt% to about 99.5wt%, for example, about 95wt% to about 99.5wt%. Based on 100wt% of the negative electrode active material layer, the content of the binder may be about 0.5wt% to about 5wt%. Based on 100wt% of the negative electrode active material layer, the content of the conductive material may be about 0.5wt% to about 5wt%. For example, the negative electrode active material layer may include about 90wt% to about 99wt% of the negative electrode active material, about 0.5wt% to about 5wt% of the binder, and about 0.5wt% to about 5wt% of the conductive material.

[0078] The binder may be used to well attach the negative electrode active material particles to each other and also to well attach the negative electrode active material to the current collector. The binder may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0079] The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0080] The aqueous binder can be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol and combinations thereof.

[0081] If an aqueous binder is used as the negative electrode binder, it may also include a cellulose compound that can impart or increase viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and alkali metal salts thereof. The alkali metal may be Na, K, and / or Li.

[0082] The dry binder may be a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0083] The conductive material is included to provide electrode conductivity (e.g., electrical conductivity), and any suitable electrically conductive material may be used as the conductive material unless it causes chemical changes (e.g., undesirable chemical changes in a rechargeable battery). Examples of the conductive material may be: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, graphene, etc.; metal-based materials in the form of metal powder and / or metal fiber, such as copper, nickel, aluminum, silver, etc.; conductive polymers (e.g., electrically conductive polymers) such as polyphenylene derivatives; or mixtures thereof.

[0084] The current collector of the negative electrode may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal (eg, electrically conductive metal), and combinations thereof, but is not limited thereto.

[0085] Electrolyte

[0086] The electrolyte for a rechargeable lithium battery includes a non-aqueous organic solvent and a lithium salt.

[0087] The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0088] The non-aqueous organic solvent may be a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, an aprotic solvent or a combination thereof.

[0089] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, valerolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents may include cyclohexanone. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles such as R-CN (wherein R is a C2-C20 straight chain, branched or cyclic hydrocarbon group, and includes a double bond, an aromatic ring or an ether group), amides (such as dimethylformamide), dioxolanes (such as 1,3-dioxolane or 1,4-dioxolane), cyclopentane, etc.

[0090] The nonaqueous organic solvent may be used alone or in a mixture of two or more types (kinds), and if two or more types (kinds) are used in a mixture, the mixing ratio may be suitably or appropriately adjusted according to suitable or desired battery performance.

[0091] In addition, if a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together and used, and the cyclic carbonate and the chain carbonate may be mixed together in a volume ratio of about 1:1 to about 1:9.

[0092] The non-aqueous organic solvent may also include an aromatic hydrocarbon organic solvent. For example, a carbonate-based solvent and an aromatic hydrocarbon organic solvent may be mixed together and used in a volume ratio of about 1:1 to about 30:1.

[0093] In order to improve the cycle life of the battery, the electrolyte may further include ethyl vinyl carbonate, vinylene carbonate and / or ethylene carbonate compounds.

[0094] Examples of the ethylene carbonate-based compound may include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0095] The lithium salt dissolved in the organic solvent supplies lithium ions in the battery, enables basic operations of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt may include a lithium ion selected from LiPF 6 , LiBF 4 、LiSbF 6 、LiAsF 6 、LiClO 4 、LiAlO 2 、LiAlCl 4 、LiPO 2 F 2 、LiCl、LiI、LiN(SO 3 C 2 F 5 ) 2 、Li(FSO 2 ) 2 N(lithium bis(fluorosulfonyl)imide, LiFSI), LiC 4 F 9 SO 3 、LiN(C x F2 x+1 SO 2 )(C y F 2y+1 SO 2)(x and y are integers of 1 to 20), one or more of lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB) and lithium bis(oxalato)borate (LiBOB).

[0096] The concentration of the lithium salt may be in the range of about 0.1 M to about 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has suitable or appropriate ion conductivity and viscosity, and thus excellent performance may be achieved, and lithium ions may be efficiently moved.

[0097] Diaphragm

[0098] Depending on the type of battery, the rechargeable lithium battery may further include a separator between the positive electrode and the negative electrode. Examples of suitable separator materials include polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof (such as polyethylene / polypropylene double-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, and polypropylene / polyethylene / polypropylene three-layer separator).

[0099] The separator may include a porous substrate and a coating layer on one or both surfaces of the porous substrate, the coating layer including an organic material, an inorganic material, or a combination thereof.

[0100] The porous substrate can be a polymer film formed by any one of a polymer selected from polyolefins (such as polyethylene and / or polypropylene), polyesters (such as polyethylene terephthalate, polybutylene terephthalate and / or polyethylene naphthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene oxides, cyclic olefin copolymers, polyphenylene sulfide, glass fibers, and TEFLON (polytetrafluoroethylene), or copolymers or mixtures of two or more thereof.

[0101] The porous substrate may have a thickness of about 1 μm to about 40 μm, for example, about 1 μm to about 30 μm, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 10 μm to about 15 μm.

[0102] The organic material may include a (meth)acryl copolymer, the (meth)acryl copolymer including a first structural unit derived from (meth)acrylamide and a second structural unit, the second structural unit including at least one selected from a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or its salt.

[0103] The inorganic material may include a 2 O 3 、SiO 2 、TiO 2 SnO 2、CeO 2 , MgO, NiO, CaO, GaO, ZnO, ZrO 2 , Y 2 O 3 、SrTiO 3 、BaTiO 3 Mg(OH) 2 , boehmite and inorganic particles of a combination thereof, but not limited thereto. The average particle size (D 50 ) can be from about 1 nm to about 2000 nm, for example, from about 100 nm to about 1000 nm, or from about 100 nm to about 700 nm.

[0104] The organic material and the inorganic material may be mixed together in one coating layer, or a coating layer including an organic material and a coating layer including an inorganic material may be stacked.

[0105] The coating layer may have a thickness of about 0.5 μm to about 20 μm, for example, about 1 μm to about 10 μm, or about 1 μm to about 5 μm.

[0106] Hereinafter, the above aspects of the embodiments of the present disclosure will be described in more detail with reference to examples. However, these are merely examples, and the present disclosure is not limited thereto.

[0107] Example 1

[0108] (1) Preparation of the first conductive material

[0109] A graphene oxide (GO) solution (solvent: distilled water) including GO at a concentration of 2.0 wt% was diluted by adding distilled water thereto, and Al 2 O 3 Nanoparticles (D 50 Here, Al was used in an amount of 10 parts by weight based on 100 parts by weight of the solid (GO) in the diluted GO solution. 2 O 3 Nanoparticles.

[0110] Subsequently, the graphene oxide (GO) is converted into reduced graphene oxide (rGO) using a hydrothermal synthesis method, and aluminum oxide nanoparticles are coated in the form of dots on the surface of the reduced graphene oxide (rGO). Thus, a first conductive material including reduced graphene oxide (rGO) as a core and an aluminum oxide nanoparticle coating layer in the form of dots on the surface of the core is obtained.

[0111] (2) Fabrication of positive electrode

[0112] 2.0 wt% of the first conductive material and 92.0 wt% of NCA (LiNi0.8 Co 0.15 Al 0.05 O 2 ), 4.0 wt % of polytetrafluoroethylene (PTFE) as a binder and 2.0 wt % of carbon black (CB) as a second conductive material are mixed together.

[0113] First, a blade mixer was used to dry mix the positive electrode active material, the binder and the second conductive material at 1000 rpm for 5 minutes, the first conductive material was added thereto, and then dry mixed again for 5 minutes. Subsequently, as the binder was fibrillated, the mixture was dry mixed for another 20 minutes at 5000 rpm. Here, no solvent was used when preparing the mixture.

[0114] The prepared mixture was put into an extruder and extruded into a sheet as a self-standing film of the positive electrode active material layer, which was attached to a current collector coated with carbon. The dry positive electrode manufactured in this way is referred to as AG-positive electrode 1.

[0115] In AG-positive electrode 1, the positive electrode active material layer has a mass of 49.4 mg / cm 2 The loading level and the mixture density of 3.6 g / cc, and in the positive electrode active material layer, the first conductive material has 444.6 μg / cm 2 The second conductive material has a loading of 444.6 μg / cm 2 of load.

[0116] (3) Manufacturing of rechargeable lithium battery cells (coin half cells)

[0117] The positive electrode and the lithium metal counter electrode were used together to make a coin half-cell. A separator made of a porous polyethylene film (thickness: about 16 μm) was set between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected therein. Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed together in a volume ratio of 3:5 and 1.1 M LiPF 6 The electrolyte solution is prepared by dissolving in the mixed solvent.

[0118] (4) Manufacturing of rechargeable lithium battery cells (symmetrical cells)

[0119] Two positive electrodes were assembled into a symmetrical pouch cell with a separator made of a porous polyethylene film (thickness: about 16 μm) in between, and then an electrolyte was injected into it. 1.1 M LiPF was dissolved in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed together in a volume ratio of 3:5. 6 to prepare the electrolyte.

[0120] Example 2

[0121] Based on 100 parts by weight of the solid (GO) in the graphene oxide solution, Al was used in an amount of 25 parts by weight. 2 O 3 Nanoparticles.

[0122] Except for this, a first conductive material, a positive electrode, and a rechargeable lithium battery cell were manufactured in the same manner as in Example 1. The dry positive electrode thus manufactured was referred to as AG-positive electrode 2 .

[0123] In the AG-positive electrode 2, the positive electrode active material layer has a mass of 49.4 mg / cm 2 The loading level and the mixture density of 3.6 g / cc, and in the positive electrode active material layer, the first conductive material has 444.6 μg / cm 2 The second conductive material has a loading of 444.6 μg / cm 2 of load.

[0124] Example 3

[0125] Based on 100 parts by weight of the solid (GO) in the graphene oxide solution, Al was used in an amount of 50 parts by weight. 2 O 3 Nanoparticles.

[0126] Except for this, a first conductive material, a positive electrode, and a rechargeable lithium battery cell were manufactured in the same manner as in Example 1. The dry positive electrode manufactured in this manner is referred to as AG-positive electrode 3.

[0127] In the AG-positive electrode 3, the positive electrode active material layer has a mass of 49.4 mg / cm 2 The loading level and the mixture density of 3.6 g / cc, and in the positive electrode active material layer, the first conductive material has 444.6 μg / cm 2 The second conductive material has a loading of 444.6 μg / cm 2 of load.

[0128] Example 4

[0129] In the same manner as in Example 1, a first conductive material was prepared.

[0130] Subsequently, 1.0 wt% of the first conductive material was mixed with 92 wt% of LiNi as a positive electrode active material. 0.8 Co 0.15 Al 0.05 O 2 , 4 wt % of polytetrafluoroethylene (PTFE) as a binder and 3.0 wt % of carbon black (CB) as a second conductive material were mixed together.

[0131] Except for this, a positive electrode and a rechargeable lithium battery cell were manufactured in the same manner as in Example 1. The dry positive electrode manufactured in this manner is referred to as AG-positive electrode 4.

[0132] In the AG-positive electrode 4, the positive electrode active material layer has a mass of 49.4 mg / cm 2 The loading level and the mixture density of 3.6 g / cc, and in the positive electrode active material layer, the first conductive material has a loading level of 222.3 μg / cm 2 The second conductive material has a loading of 666.9 μg / cm 2 of load.

[0133] Example 5

[0134] In the same manner as in Example 1, a first conductive material was prepared.

[0135] Subsequently, 3.0 wt% of the first conductive material was mixed with 92 wt% of LiNi as a positive electrode active material. 0.8 Co 0.15 Al 0.05 O 2 , 4 wt % of polytetrafluoroethylene (PTFE) as a binder and 1.0 wt % of carbon black (CB) as a second conductive material were mixed together.

[0136] Except for this, a positive electrode and a rechargeable lithium battery cell were manufactured in the same manner as in Example 1. The dry positive electrode manufactured in this manner is referred to as AG-positive electrode 5.

[0137] In the AG-positive electrode 5, the positive electrode active material layer has a mass of 49.4 mg / cm 2 The loading level and the mixture density of 3.6 g / cc, and in the positive electrode active material layer, the first conductive material has 666.9 μg / cm 2 The second conductive material has a loading of 222.3 μg / cm 2 of load.

[0138] Comparative Example 1

[0139] 92 wt % of LiNi as the positive electrode active material was mixed by using a blade mixer. 0.8 Co 0.15 Al 0.05 O 2 , 4 wt % of polytetrafluoroethylene (PTFE) as a binder and 4.0 wt % of carbon black (CB) as a second conductive material were dry-mixed together for 10 minutes (5.0 minutes×2), and then, when the binder was fiberized, they were dry-mixed together for another 20 minutes at 5000 rpm.

[0140] Except for this, a dry positive electrode was manufactured in the same manner as in Example 1. The dry positive electrode thus manufactured is referred to as a P-positive electrode.

[0141] In the P-positive electrode, the positive electrode active material layer has 49.4 mg / cm 2 The loading level and the mixture density of 3.6 g / cc, and in the positive electrode active material layer, the second conductive material has a loading level of 889.2 μg / cm 2 About load capacity.

[0142] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1 except that a P-positive electrode was used.

[0143] Comparative Example 2

[0144] 92 wt% of LiNi as the positive electrode active material 0.8 Co 0.15 Al 0.05 O 2 , 4 wt % of polytetrafluoroethylene (PTFE) as a binder, 2.0 wt % of carbon black (CB) as a second conductive material, and 2.0 wt % of graphene as a third conductive material were mixed together.

[0145] After the positive electrode active material, the binder and the second conductive material were dry-mixed together at 1000 rpm for 5 minutes by using a blade mixer, the third conductive material was added thereto and then dry-mixed together again for 5 minutes. Subsequently, when the binder was fibrillated, the mixture was dry-mixed together at 5000 rpm for another 20 minutes.

[0146] Except for this, a dry positive electrode was manufactured in the same manner as in Example 1. The dry positive electrode manufactured in this manner is referred to as a G-positive electrode.

[0147] In the G-positive electrode, the positive electrode active material layer has a mass of 49.4 mg / cm 2 The loading level and the mixture density of 3.6 g / cc, and in the positive electrode active material layer, the second conductive material has a loading level of 444.6 μg / cm 2 The third conductive material has a loading of 444.6 μg / cm 2 of load.

[0148] A rechargeable lithium battery cell was manufactured in the same manner as in Example 1, except that the G-positive electrode was used.

[0149] Evaluation Example 1: Observation of the first conductive material

[0150] The surface of the first conductive material of Example 1 was examined using a scanning electron microscope (SEM) apparatus. Figure 2), and the energy dispersive X-ray spectroscopy (EDS) mapping was analyzed using Quantum 2000 (Physical Electronics) ( Figure 3 ).

[0151] Reference Figure 2 and Figure 3 , aluminum oxide nanoparticles are coated on the surface of reduced graphene oxide in the form of dots.

[0152] Evaluation Example 2: Mechanical properties of positive electrode active material layer

[0153] The tensile strength and elongation of each of the positive electrodes of Example 1 and Comparative Examples 1 and 2 having an initial thickness of 170 μm were measured using a Shimadzu Autograph AGS-J device according to ASTM D638, and the results are shown in Figure 4 (horizontally) and Figure 5 (vertical direction).

[0154] Reference Figure 4 and Figure 5 , compared with Comparative Examples 1 and 2, in Example 1, the tensile strength and elongation are improved regardless of the horizontal direction and the vertical direction.

[0155] Evaluation Example 3: Surface resistivity of positive electrode active material layer

[0156] Each of the sheet-shaped positive electrodes of Examples 1 to 5 and Comparative Examples 1 and 2 was cut into a size of width × length = 3 cm × 10 cm to prepare a sample. A conductivity measuring device using a 4-point probe was used to measure the current by applying a 10V voltage at 47 Hz to 63 Hz to the surface of the positive electrode active material layer of the sample, and the resistance was calculated using the current. The calculated resistance was substituted into Equation 1 together with the vertical length and cross-sectional area of ​​the sample to convert it into resistivity. The results are shown in Table 1.

[0157] [Equation 1]

[0158] R=ρl / S

[0159] In equation 1,

[0160] ρ = resistance, l = length of the sample, S = cross-sectional area of ​​the sample.

[0161] Table 1

[0162]

[0163] Referring to Table 1, the resistivity of the surface of the positive electrode active material layer is reduced in Examples 1 to 5 compared to Comparative Example 1. In Examples 1 to 5, the less the content of the coating layer in the first conductive material, the lower the resistivity of the surface of the positive electrode active material layer, and the more the first conductive material is compared to the second conductive material, the lower the resistivity of the surface of the positive electrode active material layer.

[0164] Evaluation Example 4: Initial charge / discharge efficiency of a rechargeable lithium battery cell

[0165] Each of the coin half-cell type rechargeable lithium battery cells of Examples 1 to 5 and Comparative Examples 1 and 2 was constant-current charged at a current rate of 0.1C to a voltage of 4.25V (vs. Li), and then cut off at a current rate of 0.05C in a constant voltage mode of 4.25V at 25°C. Subsequently, the battery cell was discharged at a constant current rate of 0.1C to a voltage of 2.8V (vs. Li) (formation cycle).

[0166] The rechargeable lithium battery cells that passed the formation cycle were charged to a voltage of 4.4V (vs.Li) at a constant current rate of each of 0.1C, 1C, and 2C, and then cut off at a current rate of 0.05C in a constant voltage mode of 4.4V. Subsequently, the battery cells were discharged to a voltage of 2.8V (vs.Li) at a constant current rate of each of 0.1C, 1C, and 2C (first cycle). The initial charge and discharge efficiency of each of the rechargeable lithium battery cells of Examples 1 to 5 and Comparative Examples 1 and 2 was calculated according to Equation 2, and the results are shown in Table 2. The charge / discharge behavior of the rechargeable lithium battery cells of Example 1 and Comparative Examples 1 and 2 is representatively shown in Table 2. Figure 6 and Figure 7 middle.

[0167] [Equation 2]

[0168] Initial charge and discharge efficiency (%) = (first discharge capacity / first charge capacity) × 100

[0169] Table 2

[0170]

[0171]

[0172] Refer to Table 2 and Figure 6 and Figure 7 , Examples 1 to 5 exhibit improved charge / discharge behaviors at the same C rate compared to Comparative Examples 1 and 2. As the C rate increases, the charge / discharge behaviors of Examples 1 to 5 are further improved.

[0173] In Examples 1 to 5, the less the content of the coating layer in the first conductive material is, the more the charge / discharge behavior is improved, and the more the first conductive material is compared with the second conductive material, the more the charge / discharge behavior is improved.

[0174] Evaluation Example 5

[0175] Each of the pouch-type rechargeable lithium battery cells of Example 1 and Comparative Examples 1 and 2 was aged at room temperature for 40 hours to measure the ion transfer resistance (R ion ).

[0176] Independently, each of the rechargeable lithium battery coin half cells of Example 1 and Comparative Examples 1 and Comparative Examples 2 was charged to 50% SOC (battery state of charge, State of Charge) at the same C rate after being formed at a rate of 0.1C. Subsequently, each of the coin half cells of Example 1 and Comparative Examples 1 and Comparative Examples 2 was disassembled to obtain its positive electrode charged to 50% SOC, and a rechargeable lithium battery symmetrical cell was manufactured in the same manner as in Example 1 using the obtained two positive electrodes, which were aged at room temperature for 24 hours to measure the charge transfer resistance (R ct ).

[0177] These R ion and R ct As shown in Table 3 and Figure 8 and Fig. 9 middle.

[0178] Table 3

[0179] <![CDATA[R ion ]]> <![CDATA[R ct ]]> Comparative Example 1 (P-positive electrode) 15.185 13.74 Comparative Example 2 (G-positive electrode) 8.78 9.82 Example 1 (AG-positive electrode 1) 9.33 6.62

[0180] Refer to Table 3 and Figure 8 and Fig. 9 , compared with Comparative Example 1, Example 1 shows improved R ion , and Example 1 exhibits improved R compared to Comparative Example 1 and Comparative Example 2. ct .

[0181] While the subject matter of the present disclosure has been described in conjunction with what are presently considered to be practical example embodiments, it will be understood that the disclosure is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims and their equivalents.

Claims

1. An electrode for a rechargeable lithium battery, the electrode include: current collector; as well as an electrode active material layer, on the current collector, and comprising an active material, a first conductive material and a binder, The first conductive material includes: a core including graphene, graphene oxide, reduced graphene oxide or a combination thereof; and a coating layer on a surface of the core and including aluminum oxide nanoparticles.

2. The electrode according to claim 1, in: The coating layer is in the form of dots.

3. The electrode according to claim 1, in: The electrode active material layer further includes a second conductive material, and The second conductive material includes carbon black.

4. The electrode according to claim 3, in: A weight ratio of the first conductive material to the second conductive material is 1:9 to 9:

1.

5. The electrode according to claim 1, in: The binder includes polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide or a combination thereof.

6. The electrode according to claim 1, in: The active material includes lithium nickel oxide.

7. The electrode according to claim 1, in: The electrode active material layer includes 90 wt % to 99.5 wt % of the active material, 0.5 wt % to 5 wt % of the first conductive material, and 0.5 wt % to 5 wt % of the binder, based on 100 wt % of the electrode active material layer.

8. The electrode according to claim 1, in: The electrode is a positive electrode.

9. A rechargeable lithium battery comprising the electrode according to claim 1.

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