Electrodes and lithium secondary batteries containing them

Abstract

To provide electrodes with improved capacitance characteristics and lifespan characteristics. [Solution] The present invention relates to an electrode and a lithium secondary battery including the same, and more particularly to an electrode current collector, a first active material layer on the electrode current collector, and a second active material layer on the first active material layer. The first active material layer includes a first active material, a binder, and a conductive material. The second active material layer includes a second active material and a composite conductive material. The composite conductive material includes carbon nanostructures and adhesive polymers physically or chemically bonded to the surface of the carbon nanostructures.

Description

Technical Field

[0001] The present invention relates to an electrode and a lithium secondary battery including the same, and more particularly to an electrode including a composite conductive material in which an adhesive polymer is bonded to a carbon nanostructure, and a lithium secondary battery including the same.

Background Art

[0002] Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for secondary batteries with high energy density and high capacity has been rapidly increasing. Therefore, research and development for improving the performance of lithium secondary batteries are actively underway.

[0003] A lithium secondary battery includes a positive electrode and a negative electrode containing an active material capable of insertion (intercalation) and desorption (deintercalation) of lithium ions, and an electrolyte solution, and produces electrical energy through oxidation and reduction reactions when lithium ions are inserted / desorbed at the positive electrode and the negative electrode.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the present invention is to provide an electrode with improved capacity characteristics and life characteristics.

[0005] Another problem to be solved by the present invention is to provide a lithium secondary battery including the electrode.

Means for Solving the Problems

[0006] An electrode for a lithium secondary battery according to an embodiment of the present invention includes an electrode current collector, a first active material layer on the electrode current collector, and a second active material layer on the first active material layer. The first active material layer includes a first active material, a binder, and a conductive material, and the second active material layer can include a second active material and a composite conductive material. The composite conductive material can include a carbon nanostructure and an adhesive polymer physically or chemically bonded to the surface of the carbon nanostructure.

[0007] A method for manufacturing an electrode for a lithium secondary battery according to an embodiment of the present invention can include providing an electrode current collector, forming a first active material layer on the electrode current collector, and forming a second active material layer on the first active material layer. The first active material layer can include a first active material, a binder, and a conductive material, and the second active material layer can include a second active material and a composite conductive material. Manufacturing the composite conductive material can include introducing a functional group onto the surface of a carbon nanostructure and mixing an adhesive polymer and the carbon nanostructure having the functional group to produce a mixture.

[0008] A lithium secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution, and at least one of the positive electrode and the negative electrode can include the electrode described above.

Advantages of the Invention

[0009] The electrode according to the present invention can have the effect of improving the life characteristics of a lithium secondary battery because a composite conductive material in which an adhesive polymer is bonded to the surface of a carbon nanostructure is included in the upper active material layer.

Brief Description of the Drawings

[0010] [Figure 1] It is a conceptual diagram briefly showing a lithium secondary battery according to an embodiment of the present invention. [Figure 2] It is a schematic diagram showing a lithium secondary battery according to an embodiment, which has a cylindrical battery form. [Figure 3] It is a cross-sectional view showing a lithium secondary battery according to an embodiment. [Figure 4] It is a schematic diagram showing a lithium secondary battery according to an embodiment, which has a rectangular battery form. [Figure 5] It is a schematic diagram showing a lithium secondary battery according to an embodiment, which has a pouch-type battery form. [Figure 6] It is a cross-sectional view of an electrode for a secondary battery according to an embodiment of the present invention. [Figure 7] This is an enlarged view illustrating an electrode according to an embodiment of the present invention. [Figure 8] This is a cross-sectional view of an electrode according to another embodiment of the present invention. [Figure 9] This is an enlarged view illustrating an electrode according to another embodiment of the present invention. [Figure 10] This is a drawing illustrating a method for manufacturing an electrode according to one embodiment of the present invention. [Figure 11] This is a schematic diagram showing the manufacturing process of a composite conductive material according to an embodiment of the present invention. [Figure 12] This is an SEM image of a composite conductive material according to an embodiment of the present invention. [Modes for carrying out the invention]

[0011] To fully understand the structure and effects of the present invention, preferred embodiments will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and can be embodied in various forms and modified in many ways. This description of the embodiments is provided to ensure that the disclosure of the present invention is complete and to fully inform a person with ordinary skill in the art of which the invention pertains.

[0012] In this specification, when a given component is referred to as being on another component, it means that it may be formed directly on the other component, or a third component may be interposed between them. Furthermore, in the drawings, the thickness of components is exaggerated for the sake of efficient illustration of the technical content. Parts indicated by the same reference number throughout the specification represent the same component.

[0013] The embodiments described herein are explained with reference to cross-sectional and / or plan views, which are ideal illustrative diagrams of the invention. In the drawings, the thicknesses of films and regions are exaggerated for the efficient explanation of the technical content. Therefore, the regions illustrated in the drawings have schematic attributes, and the patterns of the regions illustrated in the drawings are for illustrating specific shapes of regions of the element and are not intended to limit the scope of the invention. In the various embodiments herein, terms such as first, second, third, etc., have been used to describe various components, but these components should not be limited by such terms. These terms are used merely to distinguish certain components from others. The embodiments described and illustrated herein also include complementary embodiments.

[0014] Unless otherwise specified herein, a singular noun may also include a plural noun. Furthermore, unless otherwise specified, “A or B” may mean “including A, including B, or including A and B.” As used in this specification, “comprises” and / or “comprising” does not exclude the presence or addition of one or more other components by which the referred component is located.

[0015] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0016] Unless otherwise defined herein, particle size can be the average particle size. Also, particle size refers to the average particle size (D) where the cumulative volume of the particle is 50% by volume in the particle size distribution. 50 ) means average particle size (D 50The measurement may be performed by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope or scanning electron microscope. Alternatively, the measurement may be performed using a measuring device that utilizes dynamic light scattering, and after performing data analysis to count the number of particles for each particle size range, the average particle size (D) may be calculated from this count. 50 The ) value can be obtained. Alternatively, it can be measured using the laser diffraction method. When measuring by laser diffraction, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac MT 3000), and ultrasonic waves of approximately 28 kHz are irradiated at an output of 60 W, and the average particle size (D) at the 50% reference of the particle size distribution in the measuring device is obtained. 50 It is possible to calculate ).

[0017] Unless otherwise defined herein, "*" means a portion that is linked to the same or different atoms or chemical formulas.

[0018] Figure 1 is a simplified conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention. Referring to Figure 1, the lithium secondary battery may include a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte ELL.

[0019] The positive electrode 10 and the negative electrode 20 can be separated from each other via a separator 30. The separator 30 can be placed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 can be in contact with the electrolyte ELL. The positive electrode 10, the negative electrode 20, and the separator 30 can be impregnated in the electrolyte ELL.

[0020] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. Within the electrolyte ELL, lithium ions can move towards the positive electrode 10 or the negative electrode 20 by passing through the separator 30.

[0021] positive electrode 10 The positive electrode 10 for a lithium secondary battery may include a current collector COL1 and a positive electrode active material layer AML1 formed on the current collector COL1. The positive electrode active material layer AML1 includes a positive electrode active material and may further include a binder and / or a conductive material.

[0022] As an example, the positive electrode 10 may further contain additives that can act as a sacrificial positive electrode.

[0023] The content of the positive electrode active material in the positive electrode active material layer AML1 may be 90% to 99.5% by weight relative to 100% by weight of the positive electrode active material layer AML1. The content of the binder and conductive material may be 0.5% to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer AML1.

[0024] The binder plays a role in ensuring that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well to the current collector COL1. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0025] The conductive material is used to impart conductivity to the electrode, and in the battery it constitutes, any material can be used as long as it is an electron-conductive material that does not cause a chemical change. Examples of conductive materials include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based substances containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0026] As the current collector COL1, Al can be used, but it is not limited thereto.

[0027] positive electrode active material As the positive electrode active material in the positive electrode active material layer AML1, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof with lithium can be used.

[0028] The composite oxide is a lithium transition metal composite oxide, and specific examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-pre-nickel-manganese-based oxides, or combinations thereof.

[0029] As an example, a compound represented by any one of the following chemical formulas can be used. Li 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); Lia 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 1 d G e O2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4 (0.90 ≤ a ≤ 1.8). 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, rare earth elements, 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; L 1 This is Mn, Al, or a combination of these.

[0030] As an example, the positive electrode active material may be a lithium transition metal composite oxide in which the nickel content relative to 100 mol% of the metal excluding lithium is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more, and 99 mol% or less, and is a high-nickel positive electrode active material. Since high-nickel positive electrode active materials can achieve high capacity, they can be applied to high-capacity, high-density lithium secondary batteries.

[0031] negative electrode 20 The negative electrode 20 for the lithium secondary battery includes a current collector COL2 and a negative electrode active material layer AML2 located on the current collector COL2. The negative electrode active material layer AML2 includes a negative electrode active material and may further include a binder and / or a conductive material.

[0032] For example, the negative electrode active material layer AML2 may contain 90% to 99% by weight of negative electrode active material, 0.5% to 5% by weight of binder, and 0% to 5% by weight of conductive material.

[0033] The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other and that the negative electrode active material adheres well to the current collector COL2. Non-aqueous binders, aqueous binders, dry binders, or combinations thereof can be used as binders.

[0034] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0035] The aqueous binder may be selected from styrene-styrene rubber, (meth)acrylate styrene-styrene rubber, (meth)acrylonitrile-styrene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0036] When using an aqueous binder as the negative electrode binder, it may further contain a cellulose series compound that can impart viscosity. This cellulose series compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or their alkali metal salts. As the alkali metal, Na, K, or Li can be used.

[0037] The dry binder can be a polymeric substance that can be formed into fibers, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0038] Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes in the battery can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0039] As the current collector COL2, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof can be used.

[0040] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0041] Examples of materials capable of reversibly intercalating / deintercalating lithium ions can include carbon-based negative electrode active materials such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon can include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon can include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0042] As the alloy of lithium metal, an alloy of 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 can be used.

[0043] As the material capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (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, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0044] A silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include secondary particles (core) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of these secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0045] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of this core.

[0046] Si-based or Sn-based anode active materials can be used in combination with carbon-based anode active materials.

[0047] Separator 30 Depending on the type of lithium secondary battery, a separator 30 may be present between the positive electrode 10 and the negative electrode 20. Such a separator 30 may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator can also be used.

[0048] The separator 30 may include a porous substrate and a coating layer containing organic matter, inorganic matter, or a combination thereof located on one or both sides of the porous substrate.

[0049] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or from copolymers or mixtures of two or more of these polymers.

[0050] The organic material may include polyvinylidene fluoride polymers or (meth)acrylic polymers.

[0051] The inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0052] Organic and inorganic materials can exist mixed in a single coating layer, or they can exist in a form where a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0053] Electrolyte ELL The ELL electrolyte for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0054] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of batteries can move.

[0055] Non-aqueous organic solvents may be carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvents, aprotic solvents, or combinations thereof.

[0056] Examples of carbonate-based solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0057] Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0058] As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. As ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes, etc. may be used.

[0059] Non-aqueous organic solvents can be used individually or in combination of two or more.

[0060] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and the cyclic carbonates and linear carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0061] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, enabling the basic operation of lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (where x and y are integers from 1 to 20) may contain one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluoro(oxalate) borate (LiDFOB), lithium difluorobis(oxalate) phosphate (LiDFBOP), and lithium bis(oxalate) borate (LiBOB).

[0062] Lithium-ion rechargeable battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-shaped, coin-shaped, etc., depending on their form. Figures 2 to 5 are schematic diagrams showing a lithium secondary battery according to one embodiment, where Figure 2 is a cylindrical type, Figure 3 is a cross-sectional view, Figure 4 is a prismatic type, and Figure 5 is a pouch-shaped battery. Referring to Figures 2 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator 30 can be impregnated with an electrolyte (not shown). The lithium secondary battery 100 can include a sealing member 60 that seals the case 50, as shown in Figure 2. Also, in Figure 3, the lithium secondary battery 100 can include a positive electrode lead tab 11 and a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in Figures 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for guiding the current formed in the electrode assembly 40 to the outside.

[0063] One embodiment of the present invention provides a lithium secondary battery comprising electrodes, a separator membrane, and an electrolyte. Specifically, the lithium secondary battery according to one embodiment may include a positive electrode comprising a positive electrode active material, a negative electrode comprising a negative electrode active material, and a separator membrane and an electrolyte interposed between the positive electrode and the negative electrode. At least one of the positive electrode and the negative electrode is an electrode described later, and as an example, the positive electrode may be an electrode described later.

[0064] Electrolyte for lithium secondary batteries The following describes in more detail an electrode according to one embodiment of the present invention.

[0065] Figure 6 is a cross-sectional view of an electrode for a secondary battery according to an embodiment of the present invention.

[0066] Referring to Figure 6, electrodes 10 and 20 can include an electrode current collector COL and an active material layer AML located on the electrode current collector COL.

[0067] The electrode current collector COL may include the current collector COL1 or current collector COL2 described above.

[0068] For example, the electrode current collector COL can be made from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0069] In one embodiment, Al can be used as the electrode current collector COL, but it is not limited to this.

[0070] The active material layer AML may include a first active material layer ATL1 disposed on the electrode current collector COL and a second active material layer ATL2 disposed on the first active material layer ATL1.

[0071] The first active material layer ATL1 may have a thickness TKL1, and the second active material layer ATL2 may have a thickness TKL2.

[0072] The thickness TKL of the active material layer AML can be the sum of the thickness TKL1 of the first active material layer ATL1 and the thickness TKL2 of the second active material layer ATL2.

[0073] The thickness TKL of the active material layer AML can be 10 μm to 170 μm. For example, the thickness TKL of the active material layer AML can be 10 μm or more, 11 μm or more, 15 μm or more, 20 μm or more, 30 μm or more, or 40 μm or more. For example, the thickness TKL of the active material layer AML can be 170 μm or less, 160 μm or less, 150 μm or less, 140 μm or less, 130 μm or less, 120 μm or less, 110 μm or less, 100 μm or less, 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, or 50 μm or less. If the thickness TKL of the active material layer AML satisfies the range described above, the volume change of the battery during charging and discharging can be minimized, and a battery with a long lifespan can be provided.

[0074] The thickness TKL1 of the first active material layer ATL1 can be 10 μm to 120 μm. For example, the thickness TKL1 of the first active material layer ATL1 can be 15 μm or more, 20 μm or more, 30 μm or more, or 40 μm or more. For example, the thickness TKL1 of the first active material layer ATL1 can be 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, or 40 μm or less.

[0075] The thickness TKL2 of the second active material layer ATL2 can be 10 μm to 120 μm. For example, the thickness TKL2 of the second active material layer ATL2 can be 15 μm or more, 20 μm or more, 30 μm or more, or 40 μm or more. For example, the thickness TKL2 of the second active material layer ATL2 can be 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, or 40 μm or less.

[0076] If the thickness TKL1 of the first active material layer ATL1 and the thickness TKL2 of the second active material layer ATL2 satisfy the range described above, the volume change of the battery during charging and discharging can be minimized, and a battery with a long lifespan can be provided.

[0077] As one embodiment, as the weight of the active material contained in the first active material layer ATL1 increases, TKL1 can increase. As one embodiment, as the content of the active material contained in the second active material layer ATL2 increases, TKL2 can increase.

[0078] The thickness ratio (TKL1:TKL2) of the first active material layer ATL1 and the second active material layer ATL2 can be 3:7 to 7:3. For example, the thickness ratio (TKL1:TKL2) of the first active material layer ATL1 and the second active material layer ATL2 can be 5:5. If the thickness ratio (TKL1:TKL2) of the first active material layer ATL1 and the second active material layer ATL2 satisfies the described numerical range, the adhesion force of the active material layer AML to the electrode current collector COL is improved, maximizing the capacity and energy density of the battery and at the same time achieving the ease of electrode plate processing.

[0079] FIG. 7 is an enlarged view for explaining an electrode according to an embodiment of the present invention. That is, FIG. 7 is an enlarged view of the M region in FIG. 6.

[0080] Referring to FIG. 7, the first active material layer ATL1 can include a first active material CAM1, a binder BND, and a conductive material CDM.

[0081] The first active material CAM1 can use a compound (lithium intercalation compound) capable of reversible intercalation and deintercalation of lithium. The first active material CAM1 can include a lithium composite oxide represented by the following Chemical Formula 2. [Chemical Formula 2] Li x4 M 1 y M 2 z M 3 1-y-z O 2-a X a

[0082] In the Chemical Formula 2, 0.5 ≦ x4 ≦ 1.8, 0 ≦ a ≦ 0.05, 0 < y ≦ 1, 0 ≦ z ≦ 1, and 0 ≦ y + z ≦ 1, M1 M 2 , and M 3 Each of these independently comprises one or more elements selected from metals such as Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, or La, and combinations thereof. X may contain one or more elements selected from F, S, P, or Cl.

[0083] In one embodiment, in formula 2, M 1 is Ni, and can be 0.8 ≤ y ≤ 1 and 0 ≤ z ≤ 0.2. For example, the first active material CAM1 can be LMFP (LiFePO4, lithium iron manganese phosphate), NMX (nickel manganese oxide, NiMnO2), NCA (LiNiCoAlO2, lithium nickel cobalt aluminum), or NCM (LiNiCoMnO2, lithium nickel cobalt manganese).

[0084] The binder BND can play a role in ensuring that the particles of the first active material CAM1 adhere well to each other and that the first active material CAM1 adheres well to the electrode current collector COL. For example, the binder BND may include, but is not limited to, at least one selected from the group consisting of rubber-based binders, acrylate-based binders, polyvinylidene fluoride-based binders, polyvinylpyrrolidone-based binders, acetate-based binders, polyvinyl alcohol-based binders, and cellulose-based binders.

[0085] The rubber binder may be, for example, styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), or ethylene propylene diene monomer rubber (EPDM).

[0086] The acrylate-based binder may be, for example, polyacrylic acid (PAA), polymethyl methacrylate, polyisobutyl methacrylate, polyethyl acrylate, polybutyl acrylate, or poly(2-ethylhexyl acrylate).

[0087] The polyvinylidene fluoride binder may be, for example, polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride-co-tetrafluoroethylene, polyvinylidene fluoride-co-trifluoroethylene, polyvinylidene fluoride-co-trifluorochloroethylene, polyvinylidene fluoride-co-ethylene fluoride-hexafluoropropylene (PVdF), or polyvinylidene fluoride-co-trichloroethylene.

[0088] A polyvinylpyrrolidone-based binder could be, for example, polyvinylpyrrolidone.

[0089] The nitrile binder may be, for example, polyacrylonitrile or acrylonitrilestyrene-butadiene copolymer.

[0090] The acetate binder may be, for example, polyvinyl acetate, polyethylene-co-vinyl acetate, cellulose acetate, cellulose acetate butyrate, or cellulose acetate propionate.

[0091] A polyvinyl alcohol-based binder may be, for example, polyvinyl alcohol.

[0092] Cellulose-based binders may include, for example, carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), methyl hydroxypropyl cellulose (MHPC), ethyl hydroxyethyl cellulose (EHEC), methyl ethyl hydroxyethyl cellulose (MEHEC), or cellulose gum.

[0093] The conductive material CDM is used to impart conductivity to electrodes 10 and 20. Any electronically conductive material that does not cause chemical changes can be used in the battery it is constructed from. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials such as metal powders or metal fibers of copper, nickel, aluminum, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0094] According to one embodiment, the content of the first active material CAM1 may be 90% to 99.5% by weight relative to the total weight of the first active material layer ATL1. According to one embodiment, the content of the binder BND may be 0.1% to 5% by weight relative to the total weight of the first active material layer ATL1. According to one embodiment, the content of the conductive material CDM may be 0.1% to 5% by weight relative to the total weight of the first active material layer ATL1.

[0095] If the first active material layer ATL1 satisfies the content range conditions for the first active material CAM1, the binder BND, and the conductive material CDM, the capacity and energy density of the battery can be maximized.

[0096] The second active material layer ATL2 may be formed so as to be in contact with one surface of the first active material layer ATL1. The surface of the first active material layer ATL1 may be the surface that does not come into contact with the electrode current collector COL (Figure 6). For example, electrodes 10 and 20 may be formed by sequentially stacking the electrode current collector COL (Figure 6), the first active material layer ATL1, and the second active material layer ATL2.

[0097] The second active material layer ATL2 may include the second active material CAM2 and the composite conductive material CCM.

[0098] The second active material CAM2 may be identical to the first active material CAM1 described earlier in the first active material layer ATL1. For example, the second active material CAM2 may contain a lithium composite oxide represented by the chemical formula 2 described above.

[0099] The composite conductive material CCM can ensure a lithium ion channel without binder migration occurring on the surface of the active material layer.

[0100] Composite conductive materials (CCMs) may include carbon nanostructures and adhesive polymers physically or chemically bonded to the surface of the carbon nanostructures. Chemical bonding means that the components are bonded to each other by ionic or covalent bonds. Physical bonding means that the components are simply mixed together without any change in the chemical properties of each component.

[0101] As an example, the composite conductive material CCM according to the present invention is more preferably, but not limited to, a structure in which carbon nanostructures and adhesive polymers are chemically bonded.

[0102] By using a composite conductive material CCM in which chemical bonds are formed between carbon nanostructures and adhesive polymers, the carbon nanostructures do not aggregate and are well dispersed. This improves the dispersibility of the composite conductive material CCM, allowing it to form conductive paths even in small quantities, thus enabling higher capacity. Furthermore, during battery operation, there is no aggregation or other phenomena caused by the movement of carbon nanostructures during the expansion and contraction of the active material due to charging and discharging. When using the composite conductive material CCM, the binder ratio is reduced, ensuring voids within the electrode plate, thus enabling Li + By ensuring a clear ion flow path, degradation in the thickness direction within the electrode plate due to charging and discharging is improved, potentially leading to improved lifespan and performance.

[0103] Carbon nanostructures may include carbon materials having a chain-like or elongated shape that not only exhibits excellent mechanical strength, thermal conductivity, and chemical stability, but also possess electrical conductivity.

[0104] Carbon nanostructures can be manufactured by conventional methods, such as arc discharge, laser ablation, chemical vapor deposition, and high-pressure carbon monoxide separation (HIPCO).

[0105] The size of carbon nanostructures can be in the nanometer range in diameter and in the micrometer range in length. For example, carbon nanostructures can have diameters of 5 nm to 100 nm, 15 nm to 90 nm, 20 nm to 80 nm, or 30 nm to 70 nm, and lengths of 10 μm to 100 μm, 15 μm to 90 μm, 20 μm to 80 μm, or 30 μm to 70 μm.

[0106] As an example, carbon nanostructures can include at least one selected from the group consisting of carbon nanotubes (CNTs), carbon nanofibers (CNFs), polyacetylene, graphene nanoribbons (GNRs), graphene sheets, fullerenes, nanodiamonds, mesoporous carbon, amorphous carbon, carbon quantum dots, nanoporous carbon, carbon black, nanohorns, and vitreous carbon. As an example, carbon nanostructures can include carbon nanotubes (CNTs). Carbon nanotubes (CNTs) can have single-walled (SWCNTs) or multi-walled (MWCNTs) structures.

[0107] Adhesive polymers can be organic binders that dissolve in organic solvents. Organic binders have the advantage of being able to embody a variety of properties such as adhesive strength, tensile strength, and elasticity. Any polymer that can embody an organic binder can be used as an adhesive polymer without limitation.

[0108] Adhesive polymers have no molecular weight restrictions, but they must possess functional groups such as hydroxyl groups, carboxyl groups, and amine groups, and be compatible with the active materials and other additives in the electrode composition, so there should be no problems in manufacturing the slurry. Furthermore, adhesive polymers must have electrochemically stable properties during the charging and discharging process of lithium batteries.

[0109] Adhesive polymers may include polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyethylene (PE), polyethylene glycol (PEG), polyimide (PI), polyacrylamide (PAM), polystyrene (PS), polyurethane (PU), polyvinyl vitral (PVB), polyvinyl pyrrolidine (PVP), and copolymers thereof. Adhesive polymers can be used individually or in combination of two or more.

[0110] According to one embodiment, the adhesive polymer may include at least one selected from a first structural unit represented by the following chemical formula 1-1 and a second structural unit represented by the following chemical formula 1-2.

[0111] [ka]

[0112] [ka]

[0113] In the chemical formulas 1-1 and 1-2, n and m can each be integers from 1 to 100.

[0114] For example, the first structural unit can be derived from polyvinyl alcohol (PVA). For example, the second structural unit can be derived from polyacrylonitrile (PAN).

[0115] As an example, the adhesive polymer may include at least one selected from PVA-PAN (polyvinyl alcohol-polyacrylonitrile) copolymer, PVA-PEG (polyvinyl alcohol-polyethylene glycol) copolymer, and PAA-PAN (polyacrylic acid-polyacrylonitrile) copolymer.

[0116] The adhesive polymer can be included in the composite conductive material CCM in a weight ratio of 0.1% to 15% by weight relative to 100% by weight of the total amount. If the content of the adhesive polymer in the composite conductive material CCM exceeds the above range, it may act as a resistor, increasing the resistance inside the electrode. If the content of the adhesive polymer in the composite conductive material CCM is below the above range, the battery performance may be reduced because the trace amount of polymer cannot uniformly distribute the electrode material.

[0117] According to one embodiment, the second active material layer ATL2 does not need to contain the binder BND or conductive material CDM used in the first active material layer ATL1. That is, the content of the binder BND or conductive material CDM in the second active material layer ATL2 may be 0.

[0118] In other embodiments, the second active material layer ATL2 may contain trace amounts of binder BND or conductive material CDM, which are separated from the composite conductive material CCM. For example, the content of binder BND in the second active material layer ATL2 may be 0.1% by weight or less, and the content of conductive material CDM may be 0.1% by weight or less. That is, since the second active material layer ATL2 contains only very small amounts of binder BND or conductive material CDM, it can be considered as if the binder BND or conductive material CDM has been substantially omitted.

[0119] The binder BND and conductive material CDM in the first active material layer ATL1 may be composed as additives to the first active material layer ATL1. The second active material layer ATL2 may contain a composite conductive material CCM that corresponds to the role of the additives in the first active material layer ATL1.

[0120] The content of additives in the first active material layer ATL1 may be greater than the content of the composite conductive material CCM in the second active material layer ATL2. This is because the composite conductive material CCM contains a structure in which carbon nanostructures and adhesive polymers are closely bonded, allowing for the maximization of conductivity and adhesion even in small amounts.

[0121] According to one embodiment, the content of additives in the first active material layer ATL1 may be 1 to 3 times greater than the content of composite conductive material CCM in the second active material layer ATL2.

[0122] According to one embodiment, the porosity of the second active material layer ATL2 may be greater than that of the first active material layer ATL1. For example, the porosity of the first active material layer ATL1 may be 10% to 30%, while the porosity of the second active material layer ATL2 may be 15% to 40%.

[0123] The second active material layer ATL2 can have a relatively larger porosity than the first active material layer ATL1 by using a composite conductive material CCM, which integrates carbon nanostructures and adhesive polymers, instead of using a binder BND and a conductive material CDM.

[0124] Therefore, the migration pathway of lithium ions within the second active material layer ATL2 is shortened, which can facilitate the movement of lithium ions within the second active material layer ATL2. In other words, the ionic conductivity of the second active material layer ATL2 can be improved.

[0125] On the other hand, the first active material layer ATL1 has a relatively higher adhesive strength compared to the second active material layer ATL2, and a relatively lower porosity compared to the second active material layer ATL2, as the binder BND is uniformly dispersed within the first active material layer ATL1.

[0126] According to one embodiment, the content of the second active material CAM2 can be 90% to 99.5% by weight relative to the total weight of the second active material layer ATL2. If the second active material layer ATL2 satisfies the content range conditions for the second active material CAM2, it is possible to maximize the capacity and energy density of the battery while simultaneously achieving ease of electrode plate processing.

[0127] According to one embodiment, the content of the composite conductive material CCM can be 0.5% to 5% by weight relative to the total weight of the second active material layer ATL2. If the content of the composite conductive material CCM in the second active material layer ATL2 exceeds the above range, the resistance of the electrodes may increase, potentially reducing the stability and performance of the battery. If the second active material layer ATL2 does not contain the composite conductive material CCM, or if the content of the composite conductive material CCM in the second active material layer ATL2 is less than the above range, it is difficult to maximize the effect of improving ion conductivity.

[0128] Figure 8 is an enlarged view illustrating an electrode according to another embodiment of the present invention. Specifically, Figure 9 is an enlarged view of the N region in Figure 8. In this embodiment, detailed explanations of technical features that overlap with those previously described with reference to Figures 6 and 7 are omitted, and the differences are explained in detail.

[0129] Referring to Figures 8 and 9, electrodes 10', 20' according to other embodiments of the present invention may include a single layer of active material AML'.

[0130] The electrodes 10' and 20' may include an electrode current collector COL' and an active material layer AML' located on the electrode current collector COL'.

[0131] In one embodiment, Al can be used as the electrode current collector COL', but it is not limited to this.

[0132] The active material layer AML' may be formed so as to be in contact with one surface of the electrode current collector COL'. The surface of the active material layer AML' may be the surface in contact with the electrode current collector COL'. For example, electrodes 10' and 20' may be formed by sequentially stacking the electrode current collector COL' and the active material layer AML'.

[0133] The active material layer AML' is provided on the electrode current collector COL' and may have a thickness TKL'. For example, the thickness TKL' of the active material layer AML' can be 10 μm to 170 μm.

[0134] Referring to Figure 9, the active material layer AML' may include the active material CAM', the composite conductive material CCM', the binder BND', and the conductive material CDM'.

[0135] The active material CAM' may be the same as the first active material CAM1 or the second active material CAM2 mentioned above. The binder BND' may be the same as the binder BND mentioned above. The conductive material CDM' may be the same as the conductive material CDM mentioned above. The composite conductive material CCM' may be the same as the composite conductive material CCM mentioned above.

[0136] According to one embodiment, the content of the active material CAM' may be 90% to 99.5% by weight relative to the total weight of the active material layer ATL'. According to one embodiment, the content of the binder BND' may be 0.5% to 5% by weight relative to the total weight of the active material layer ATL'. According to one embodiment, the content of the conductive material CDM' may be 0.1% to 5% by weight relative to the total weight of the active material layer ATL'. According to one embodiment, the content of the composite conductive material CCM' may be 0.1% to 5% by weight relative to the total weight of the active material layer AML'.

[0137] If the active material layer ATL' satisfies the content range conditions for the active material CAM', the binder BND', the conductive material CDM', and the composite conductive material CCM', the battery capacity and energy density can be maximized.

[0138] The active material layer AML' may include a first portion RG1 adjacent to the electrode current collector COL' and a second portion RG2 adjacent to the surface of the active material layer AML'. For example, the first portion RG1 may be the region in which the active material layer AML' is in contact with the electrode current collector COL'. The second portion RG2 may be the region in which the active material layer AML' is not in contact with the electrode current collector COL'.

[0139] The first part RG1 of the active material layer AML' may contain the active material CAM', the binder BND', and the conductive material CDM'. The second part RG2 of the active material layer AML' may contain the active material CAM' and the composite conductive material CCM'. That is, the composite conductive material CCM' can only be contained in the second part RG2 of the active material layer AML'.

[0140] According to one embodiment, the active material CAM' and the composite conductive material CCM' may be included in the second portion RG2 in a weight ratio of 99.5:0.5.

[0141] If the second part RG2 does not contain the composite conductive material CCM', or if the content of the composite conductive material CCM' deviates from the range described above, it is difficult to maximize the ionic conductivity improvement effect.

[0142] In one embodiment, when electrodes 10' and 20' have a single layer of active material AML', adding a composite conductive material CCM' to the second portion RG2 improves the adhesion between the electrode current collector COL' and the active material layer AML', while simultaneously ensuring a lithium ion channel on the surface of the active material layer AML'.

[0143] Electrode manufacturing method Figure 10 is a diagram illustrating a method for manufacturing an electrode according to one embodiment of the present invention.

[0144] Referring to Figure 10, a method for manufacturing an electrode according to one embodiment of the present invention may include providing an electrode current collector COL, forming a first active material layer ATL1 on the electrode current collector COL, and forming a second active material layer ATL2 on the first active material layer ATL1.

[0145] In one embodiment, the first active material layer ATL1 may include the first active material CAM1, binder BND, and conductive material CDM as described in Figure 7. The second active material layer ATL2 may include the second active material CAM2 and composite conductive material CCM as described in Figure 7.

[0146] Since the electrode current collector COL, the first active material layer ATL1, and the second active material layer ATL2 are identical in configuration to the electrodes 10 and 20 in the embodiment described earlier, a detailed explanation will be omitted below.

[0147] The composite conductive material CCM may include carbon nanostructures and adhesive polymers physically or chemically bonded to the surface of the carbon nanostructures.

[0148] Carbon nanostructures may include at least one selected from the group consisting of carbon nanotubes (CNTs), carbon nanofibers (CNFs), polyacetylene, graphene nanoribbons (GNRs), graphene sheets, fullerenes, nanodiamonds, mesoporous carbon, amorphous carbon, carbon quantum dots, nanoporous carbon, carbon black, nanohorns, and vitreous carbon.

[0149] For example, carbon nanostructures can include carbon nanotubes (CNTs).

[0150] The adhesive polymer may include at least one selected from the group consisting of polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyethylene (PE), polyethylene glycol (PEG), polyimide (PI), polyacrylamide (PAM), polystyrene (PS), polyurethane (PU), polyvinyl vitral (PVB), and polyvinyl pyrrolidine (PVP).

[0151] As an example, the adhesive polymer may include at least one selected from PVA-PAN (polyvinyl alcohol-polyacrylonitrile) copolymer, PVA-PEG (polyvinyl alcohol-polyethylene glycol) copolymer, and PAA-PAN (polyacrylic acid-polyacrylonitrile) copolymer.

[0152] Manufacturing composite conductive materials (CCMs) may include introducing functional groups to the surface of carbon nanostructures, mixing an adhesive polymer with the functional group-containing carbon nanostructures to produce a mixture, and stirring and heat-treating the mixture.

[0153] Figure 11 is a schematic diagram showing the manufacturing process of the composite conductive material chemically bonded with the adhesive polymer of the present invention. Referring to Figure 11, the manufacturing method of the composite conductive material is described below.

[0154] Carbon nanostructures may include a pretreatment step to introduce functional groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH) onto the surface of the carbon nanostructure for chemical modification.

[0155] Introducing functional groups may include a pretreatment step using at least one of the following methods: wet treatment using strong acids, plasma treatment, and dry treatment using vacuum ultraviolet irradiation.

[0156] The preparation of a mixture may include mixing an adhesive polymer with a carbon nanostructure having functional groups. For example, the prepared mixture may be obtained by adding a carbon nanostructure to a solvent containing an adhesive polymer. The prepared mixture can undergo a chemical reaction to induce chemical bonding.

[0157] The mixture may be stirred and heat-treated for the chemical reaction. For example, stirring and heat treatment may be carried out at temperatures in the range of 60°C to 90°C.

[0158] As an example, the mixture may further contain a crosslinking agent and a catalyst to activate the chemical reaction.

[0159] Finally, the reaction-completed mixture can be dried to produce a composite conductive material CCM in which carbon nanostructures and adhesive polymers are chemically bonded.

[0160] According to other embodiments, the composite conductive material CCM may be manufactured by a self-assembly method in which an adhesive polymer and a carbon nanostructure having functional groups are mixed to produce a mixture, and the mixture is vaporized or gelled to induce the carbon nanostructure and adhesive polymer to align naturally. The composite conductive material CCM manufactured by self-assembly can form a specific structure in which the carbon nanostructure is arranged between adhesive polymer chains.

[0161] When carbon nanostructures with introduced functional groups are simply mixed with adhesive polymers to be used as composite conductive materials (CCM), chemical bonding is less likely to be induced between them during the electrode manufacturing process. Even if physical bonding is induced, the bonding strength is lower than that of chemical bonding, which can reduce the effect of suppressing the aggregation of carbon nanostructures. Here, physical bonding means that the components are simply mixed together and the chemical properties of each component do not change.

[0162] In one embodiment, the composite conductive material CCM improves the dispersibility of carbon nanostructures by forming chemical bonds between carbon nanostructures and adhesive polymers, enabling the formation of conductive pathways even with small amounts. As a result, the amount of active material in the active material layer can be increased, thus enabling higher capacity. Furthermore, during lithium battery operation, the conductive pathways can be maintained without aggregation of carbon nanostructures even during the expansion and contraction of the active material due to charging and discharging, thereby improving the lifespan characteristics of the lithium battery.

[0163] According to one embodiment, at least one of the processes of forming the first active material layer ATL1 and the second active material layer ATL2 may be carried out in a wet process or a dry process. In one embodiment, the first active material layer ATL1 may be formed in a wet process and the second active material layer ATL2 may be formed in a dry process. In another embodiment, the first active material layer ATL1 may be formed in a dry process and the second active material layer ATL2 may also be formed in a dry process. However, it is not limited thereto.

[0164] The wet process may involve mixing the active materials CAM1 and CAM2, the binder BND, the conductive material CDM, and the composite conductive material CCM in a solvent to produce an electrode mixture, which is then applied to the electrode current collector COL, dried, and rolled. The solvent in the slurry may be a solvent commonly used in the art, and may include at least one of the following: dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, and combinations thereof.

[0165] The dry process may involve dry mixing the dry active materials CAM1 and CAM2, the binder BND, the conductive material CDM, and the composite conductive material CCM without a solvent to produce an electrode mixture, and then placing the mixture on the electrode current collector COL and rolling it.

[0166] Subsequently, a roll pressing process, a slitting process, and a notching process can be sequentially performed on the positive electrode 10 or negative electrode 20 manufactured through the process described above. The positive electrode 10, the separator 30, and the negative electrode 20 can be stacked, and the electrolyte ELL can be provided to manufacture the lithium secondary battery according to the present invention.

[0167] Examples and comparative examples of the present invention are described below. However, the examples described below are merely one embodiment of the present invention, and the present invention is not limited to the examples described below.

[0168] Example 1: Fabrication of an electrode containing a double active material layer 1) Manufacturing of composite conductive materials Two g of multi-walled carbon nanotubes (Multi-walled CNTs) with a diameter of approximately 1 nm and a length of approximately 25 μm were pre-treated in 300 ml of a 20 wt% nitric acid solution at 40°C for 24 hours. Next, one g of the treated CNTs was immersed in 200 ml of a solution of concentrated sulfuric acid and concentrated sulfuric acid mixed in a 3:1 (v / v%) ratio. The CNTs were then sonicated at room temperature for 3 hours, followed by stirring at 70°C for 6 hours. After that, the acid solution adhering to the CNTs was thoroughly removed by filtering and multiple washes with pure water. Finally, the CNTs were dried in a vacuum oven at 80°C for 24 hours to produce CNTs with introduced carboxyl groups (-COOH).

[0169] 3 g of adhesive polymer and 27 g of anhydrous DMAc (dimethyl acetamide) were mixed in a reaction vessel and stirred and heated at 100°C for 6 hours under a nitrogen atmosphere to completely dissolve the adhesive polymer in the DMAc. The adhesive polymer used was a PVA-PAN (polyvinyl alcohol-polyacrylonitrile) copolymer.

[0170] After the reaction vessel was cooled to room temperature, 30 g of CNTs with carboxyl groups introduced was added, sonicated for 10 minutes, and then stirred for 1 hour. Subsequently, the temperature of the reaction vessel was raised to 90°C and the reaction was stirred for 24 hours. After the reaction was complete, the solution in the reaction vessel was poured into 200 ml of ethyl alcohol solution, the reactants were precipitated, and then the mixture was filtered, washed, and dried to produce a composite conductive material in which an adhesive polymer was bonded to the surface of the CNTs.

[0171] 2) Cathode slurry manufacturing A first active material slurry was prepared by dispersing the positive electrode active material, conductive material, and binder in N-methylpyrrolidone in a weight ratio of 100:0.2:0.9.

[0172] A second active material slurry was prepared by dispersing the positive electrode active material and the manufactured composite conductive material in N-methylpyrrolidone in a weight ratio of 100:1.

[0173] In Example 1, LiNiCoAlO2 was used as the positive electrode active material, carbon nanotubes (CNTs) were used as the conductive material, and polyvinylidene fluoride (PVdF) was used as the binder.

[0174] 3) Cathode Manufacturing The manufactured first active material slurry was applied to and dried on a 12 μm thick aluminum (Al) thin film, which served as the positive electrode current collector, to form a first active material layer approximately 30 μm thick. The manufactured second active material slurry was applied to and dried on the first active material layer to form a second active material layer approximately 30 μm thick. A positive electrode was manufactured by performing a roll press, in which the aluminum current collector, the first active material layer, and the second active material layer were sequentially laminated.

[0175] 4) Manufacturing of lithium-ion batteries A negative electrode active material slurry was prepared by mixing 98% by weight of a graphite-Si composite in a weight ratio of 92:8, 1% by weight of styrene-styrene rubber (SBR), and 1% by weight of carboxymethylcellulose (CMC). The mixture was then added to distilled water and stirred for 60 minutes using a mechanical stirrer. The slurry was then coated to a thickness of approximately 60 μm onto a 10 μm thick copper current collector using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, dried again under vacuum and 120°C conditions for 4 hours, and then rolled to produce the negative electrode.

[0176] An electrolyte was prepared by dissolving 1.15 M LiPF6 in a non-aqueous organic solvent mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:40:40.

[0177] An electrode assembly was manufactured by assembling a positive electrode, a negative electrode, and a 16 μm thick polyethylene separator, and then a lithium secondary battery was manufactured by injecting an electrolyte.

[0178] Example 2 The positive electrode and lithium secondary battery were manufactured in the same manner as in Example 1, except that the weight ratio of the positive electrode active material and the composite conductive material in the second active material slurry was set to 100:0.5 during the positive electrode manufacturing process.

[0179] Example 3 The cathode and lithium secondary battery were manufactured using the same method as in Example 1, except that a PVA-PEG (polyvinyl alcohol-polyethylene glycol) copolymer was used instead of a PVA-PAN copolymer as the adhesive polymer during the production of the composite conductive material.

[0180] Example 4 The cathode and lithium secondary battery were manufactured using the same method as in Example 1, except that a PAA-PAN (polyacrylic acid-polyacrylonitrile) copolymer was used instead of a PVA-PAN copolymer as the adhesive polymer during the production of the composite conductive material.

[0181] Comparative Example 1: Manufacturing of a positive electrode containing a single layer of active material A first active material slurry was prepared by dispersing the positive electrode active material, conductive material, and binder in N-methylpyrrolidone in a weight ratio of 100:0.2:0.9.

[0182] In Comparative Example 1, LiNiCoAlO2 was used as the positive electrode active material, carbon nanotubes (CNTs) were used as the conductive material, and polyvinylidene fluoride (PVdF) was used as the binder.

[0183] The manufactured first active material slurry was applied to and dried on a 12 μm thick aluminum (Al) thin film, which served as the positive electrode current collector, to form a first active material layer approximately 30 μm thick. A positive electrode was then manufactured by roll pressing, in which the aluminum current collector and the first active material layer were sequentially laminated.

[0184] A lithium secondary battery was manufactured using the positive electrode produced in Comparative Example 1, in the same manner as in Example 1.

[0185] Comparative Example 2 The positive electrode and lithium secondary battery were manufactured in the same manner as in Comparative Example 1, except that the composition of the first active material slurry was mixed so that the weight ratio of the positive electrode active material and the composite conductive material was 100:10. In Comparative Example 2, the same composite conductive material as used in Example 1 was used.

[0186] The positive electrode compositions for the examples and comparative examples are shown in Table 1 below.

[0187] [Table 1]

[0188] Evaluation Example 1: Confirmation of Composite Conductive Material Structure The composite conductive material manufactured in Example 1 was photographed using a scanning electron microscope (SEM).

[0189] Figure 12 is an SEM image of the composite conductive material manufactured in Example 1.

[0190] Referring to Figure 12, when the composite conductive material manufactured in Example 1 is observed with a scanning electron microscope (SEM), it can be seen that the adhesive polymer is located within a range of 0.01 μm to 500 μm from the surface of the carbon nanostructure.

[0191] Evaluation Example 2: Adhesion Strength Evaluation The peel strength of the cathodes manufactured in the examples and comparative examples was measured according to the method specified in ASTM D3330. The instruments used for measurement were a UTM and an Instron 3345.

[0192] Specifically, positive electrode plates with active material layers on both sides, manufactured in the examples and comparative examples, were cut to a size of 25 mm x 150 mm, and 20 test pieces were prepared for each. At room temperature, adhesive was coated onto a glass substrate, the positive electrode plate was attached to the adhesive, roll-pressed, one end of the positive electrode plate was folded 180°, and the force applied was measured while pulling in the opposite direction of the end at a speed of 100 mm / min. The evaluation results are shown in Table 2 below.

[0193] [Table 2]

[0194] As shown in Table 2, the peel strength was increased in the positive electrode of the embodiment compared to the positive electrode of the comparative example. Therefore, it was confirmed that the positive electrode of the embodiment has significantly improved adhesive force between the positive electrode active material layer and the current collector compared to the positive electrode of Comparative Example 1.

[0195] Evaluation Example 3: Charge / Discharge Cycle Characteristics Evaluation The lithium secondary batteries manufactured in the examples and comparative examples were subjected to 300 cycles under 25°C and 0.5C charging (CC / CV, 4.25V, 0.05C Cut-off) / 0.5C discharging (CC, 2.8V Cut-off) conditions. The discharge capacity was measured, and the capacity retention rate was calculated. The results are shown in Table 3 below. The capacity retention rate was calculated using Equation 1 below. [Formula 1] Capacity retention rate (%) = (Discharge capacity after 300 cycles / Initial discharge capacity) * 100

[0196] [Table 3]

[0197] Referring to Table 3, it was confirmed that when using electrodes according to embodiments of the present invention (Examples 1-4), the capacity retention rate in response to charge-discharge cycles at room temperature is improved compared to electrodes according to comparative examples.

[0198] Evaluation Example 4: Rapid Charging Characteristics Evaluation The lithium secondary batteries manufactured in the examples and comparative examples were charged at 25°C at 0.2C, 0.5C, 1C, 2C, and 3C CC-CV (Constant Current-Constant Voltage), respectively, and then discharged at 1 / 3C. The rapid charging characteristics were calculated and the results are shown in Table 4 below. The rapid charging characteristics were calculated using Equation 2 below. [Formula 2] Quick charging characteristics (%)=(2C CC charging capacity / 0.2C CC charging capacity)*100

[0199] [Table 4]

[0200] Referring to Table 4, it was confirmed that when using electrodes according to embodiments of the present invention (Examples 1-4), the rapid charging characteristics at room temperature are improved compared to the electrodes according to comparative examples.

[0201] While preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and can be implemented in various ways within the scope of the claims, the detailed description of the invention, and the attached drawings, which naturally also fall within the scope of the present invention. [Explanation of symbols]

[0202] 100 Lithium-ion rechargeable batteries 10 positive electrode 11 Positive lead tab 12 Positive terminal 20 negative electrode 21 Negative lead tab 22 Negative terminal 30 Separators 40 Electrode assembly 50 cases 60 Sealing member 70 electrode tabs 71 Positive Tab 72 Negative Electrode Tabs

Claims

1. Electrode current collector and The first active material layer on the electrode current collector, The invention comprises a second active material layer on the first active material layer, The first active material layer comprises a first active material, a binder, and a conductive material. The second active material layer comprises the second active material and a composite conductive material. The composite conductive material includes carbon nanostructures and adhesive polymers physically or chemically bonded to the surface of the carbon nanostructures. Electrodes for lithium-ion secondary batteries.

2. The carbon nanostructures include carbon nanotubes (CNTs), carbon nanofibers (CNFs), polyacetylene, graphene nanoribbons (GNRs), graphene sheets, fullerenes, nanodiamonds, mesoporous carbon, amorphous carbon, carbon quantum dots, nanoporous carbon, and carbon black. It includes at least one selected from the group consisting of Black, nanohorns, and vitreous carbon. The electrode for a lithium secondary battery according to claim 1.

3. The adhesive polymer comprises at least one selected from the group consisting of polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyethylene (PE), polyethylene glycol (PEG), polyimide (PI), polyacrylamide (PAM), polystyrene (PS), polyurethane (PU), polyvinyl vitral (PVB), and polyvinyl pyrrolidine (PVP). The electrode for a lithium secondary battery according to claim 1.

4. The adhesive polymer comprises a first structural unit represented by the following chemical formula 1-1, and An electrode for a lithium secondary battery according to claim 1, comprising at least one of the second structural units represented by the following chemical formulas 1-2. 【Chemistry 1】 【Chemistry 2】 In the chemical formulas 1-1 and 1-2, n and m are integers from 1 to 100.

5. The adhesive polymer is contained in a weight ratio of 0.1% to 80% by weight relative to 100% by weight of the total amount of the composite conductive material. The electrode for a lithium secondary battery according to claim 1.

6. The electrode for a lithium secondary battery according to claim 1, wherein when the composite conductive material is observed with a scanning electron microscope (SEM), the adhesive polymer is located within a 500 μm range from the surface of the carbon nanostructure.

7. The electrode for a lithium secondary battery according to claim 1, wherein the content of the composite conductive material in the second active material layer is 0.5% by weight to 5% by weight.

8. Each of the first active material and the second active material is: An electrode for a lithium secondary battery according to claim 1, represented by the following chemical formula 2. [Chemical 2] Li x4 M 1 y M 2 z M 3 1-y-z O 2-a X a In the aforementioned chemical formula 2, 0.5 ≤ x 4 ≤ 1.8, 0 ≤ a ≤ 0.05, 0 < y ≤ 1, 0 ≤ z ≤ 1, and 0 ≤ y + z ≤ 1. M 1 M 2 , and M 3 Each independently comprises one or more elements selected from metals such as Ni, Co, Mn, Al, B, Ba, Ca, Ce, Cr, Fe, Mo, Nb, Si, Sr, Mg, Ti, V, W, Zr, or La, and combinations thereof. X contains one or more elements selected from F, S, P, or Cl.

9. Each of the first and second active materials is LMFP (LiFePO 4 (Lithium manganese iron phosphate), NMX (nickel manganese oxide, NiMnO) 2 ), NCA (LiNiCoAlO 2 (Lithium nickel cobalt aluminum), or NCM (LiNiCoMnO) 2 It includes at least one selected from the group consisting of lithium nickel cobalt manganese, The conductive material comprises at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube. The binder comprises at least one selected from rubber-based binders, acrylate-based binders, polyvinylidene fluoride-based binders, polyvinylpyrrolidone-based binders, acetate-based binders, polyvinyl alcohol-based binders, and cellulose-based binders. The electrode for a lithium secondary battery according to claim 1.

10. The porosity of the second active material layer is greater than that of the first active material layer. The electrode for a lithium secondary battery according to claim 1.

11. The binder and the conductive material in the first active material layer constitute additives to the first active material layer. The content of the additive in the first active material layer is 1 to 3 times greater than the content of the composite conductive material in the second active material layer. The electrode for a lithium secondary battery according to claim 1.

12. The aforementioned second active material layer is one in which the binder is omitted. The electrode for a lithium secondary battery according to claim 1.

13. To provide an electrode current collector, Forming a first active material layer on the electrode current collector, This includes forming a second active material layer on the first active material layer, The first active material layer comprises a first active material, a binder, and a conductive material. The second active material layer comprises the second active material and a composite conductive material. Manufacturing the aforementioned composite conductive material is Introducing functional groups to the surface of carbon nanostructures, The process includes mixing an adhesive polymer and the carbon nanostructure having a functional group to produce a mixture, A method for manufacturing electrodes for lithium secondary batteries.

14. The process for producing the composite conductive material further includes stirring and heat-treating the mixture. A method for manufacturing an electrode for a lithium secondary battery according to claim 13.

15. The composite conductive material includes carbon nanostructures and adhesive polymers physically or chemically bonded to the surface of the carbon nanostructures. A method for manufacturing an electrode for a lithium secondary battery according to claim 13.

16. Introducing the aforementioned functional group means At least one of the following methods is used: wet treatment using strong acids, plasma treatment, and dry treatment using vacuum ultraviolet irradiation. A method for manufacturing an electrode for a lithium secondary battery according to claim 13.

17. The functional group comprises at least one of a carboxyl group (-COOH) and a hydroxyl group (-OH). A method for manufacturing an electrode for a lithium secondary battery according to claim 13.

18. The carbon nanostructures include carbon nanotubes (CNTs), carbon nanofibers (CNFs), polyacetylene, graphene nanoribbons (GNRs), graphene sheets, fullerenes, nanodiamonds, mesoporous carbon, amorphous carbon, carbon quantum dots, nanoporous carbon, and carbon black. It includes at least one selected from the group consisting of Black, nanohorns, and vitreous carbon. The adhesive polymer comprises at least one selected from the group consisting of polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyethylene (PE), polyethylene glycol (PEG), polyimide (PI), polyacrylamide (PAM), polystyrene (PS), polyurethane (PU), polyvinyl vitral (PVB), and polyvinyl pyrrolidine (PVP). A method for manufacturing an electrode for a lithium secondary battery according to claim 13.

19. The adhesive polymer comprises a first structural unit represented by the following chemical formula 1-1, and A method for manufacturing an electrode for a lithium secondary battery according to claim 13, comprising at least one of the second structural units represented by the following chemical formulas 1-2. 【Transformation 3】 【Chemistry 4】 In the chemical formulas 1-1 and 1-2, n and m are integers from 1 to 100.

20. Positive electrode and, The negative electrode and, A separation membrane interposed between the positive electrode and the negative electrode, It contains an electrolyte, A lithium secondary battery wherein at least one of the positive electrode and the negative electrode is the electrode described in claim 1.

Images