Negative electrode for lithium rechargeable battery, lithium rechargeable battery comprising the same, and method of preparing negateive electrode

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, a lithium secondary battery including the same, and a method for manufacturing the same. More specifically, the negative electrode comprises a current collector; an active material layer on the current collector; and photoresist particles on the surface of the active material layer, wherein the active material layer comprises an intaglio pattern formed on the upper surface of the active material layer.

Description

Technology Field

[0001] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same, and more specifically, to a negative electrode for a lithium secondary battery utilizing a photoresist, a lithium secondary battery including the same, and a method for manufacturing the same. Background Technology

[0003] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of lithium ion intercalation and deintercalation, and an electrolyte, which produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated or deintercalated from the positive and negative electrodes. The problem to be solved

[0005] The problem to be solved by the present invention is to provide an electrode for a lithium secondary battery having a reduced ionic resistance of lithium ions by including an intaglio pattern on a negative electrode active material, and a lithium secondary battery including the same.

[0006] Another problem that the present invention aims to solve is, The present invention provides a negative electrode for a lithium secondary battery with improved safety and capacity retention characteristics by suppressing the detachment of the active material during the intaglio pattern processing process through the formation of a photoresist layer, and a lithium secondary battery including the same. means of solving the problem

[0008] A method for manufacturing a negative electrode for a lithium secondary battery according to the concept of the present invention comprises: forming a negative electrode active material layer on a negative electrode current collector; and forming a photoresist layer on the negative electrode active material layer.

[0009] The method may include performing an intaglio pattern processing process on the photoresist layer to form an intaglio pattern on the cathode active material layer; and selectively removing the photoresist layer.

[0010] According to another concept of the present invention, a negative electrode for a lithium secondary battery may comprise a negative electrode current collector; and a negative electrode active material layer provided on the negative electrode current collector. The negative electrode active material layer may comprise photoresist particles on a surface and may include an intaglio pattern formed on the upper surface of the negative electrode active material layer.

[0011] According to another concept of the present invention, a lithium secondary battery comprises a positive electrode; a negative electrode; and the negative electrode comprises a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer comprises photoresist particles on a surface and includes an intaglio pattern formed on the upper surface of the negative electrode active material layer, and may include a separator between the positive electrode and the negative electrode. Effects of the invention

[0013] The negative electrode for a lithium secondary battery according to the present invention and the lithium secondary battery including the same can reduce the resistance to lithium ion movement by including a negative electrode active material layer having an intaglio pattern formed thereon. In addition, the detachment of the negative electrode active material can be suppressed by performing the intaglio pattern processing process after forming a photoresist layer. As a result, the lithium secondary battery according to the present invention can have safety and excellent capacity. Brief explanation of the drawing

[0015] FIG. 1 is a conceptual diagram briefly illustrating a lithium secondary battery according to embodiments of the present invention. FIGS. 2 to 5 are cross-sectional views schematically illustrating a lithium secondary battery according to one embodiment. FIG. 6 is a cross-sectional view showing a lithium secondary battery according to embodiments of the present invention. Figure 7 is an enlarged cross-sectional view of the M region of Figure 6. Figure 8 is an enlarged plan view of the M region of Figure 6. Figure 9 is an enlarged plan view of area A of Figure 8. FIGS. 10 and 11 are enlarged views relating to an embodiment of an intaglio pattern that can be formed on an active material layer of the present invention. FIGS. 12, FIGS. 13 and FIGS. 14 are cross-sectional views illustrating the process of manufacturing a cathode according to an embodiment of the present invention. FIG. 15 is a plan view of a negative electrode active material layer according to embodiments of the present invention. Specific details for implementing the invention

[0016] In order to fully understand the structure and effects of the present invention, preferred embodiments of the present invention are described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various modifications can be made. The description of these embodiments is provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention.

[0017] In this specification, when a component is described as being on another component, it means that it may be formed directly on the other component or that a third component may be interposed between them. Additionally, in the drawings, the thicknesses of the components are exaggerated for the effective description of the technical content. Throughout the specification, parts indicated by the same reference numeral represent the same components.

[0018] Unless otherwise specified in this specification, the singular form may also include the plural. Additionally, unless otherwise specified, "A or B" may mean "comprising A, comprising B, or comprising A and B." As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components to the mentioned components.

[0019] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0020] FIG. 1 is a conceptual diagram briefly illustrating a lithium secondary battery according to embodiments of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode (10), a negative electrode (20), a separator (30), and an electrolyte (ELL).

[0021] The positive electrode (10) and the negative electrode (20) may be spaced apart from each other with a separator (30) in between. The separator (30) may be placed between the positive electrode (10) and the negative electrode (20). The positive electrode (10), the negative electrode (20), and the separator (30) may come into contact with an electrolyte (ELL). The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated within the electrolyte (ELL).

[0022] The electrolyte (ELL) may be a medium for transferring lithium ions between the positive electrode (10) and the negative electrode (20). Within the electrolyte (ELL), the lithium ions may pass through a separator (30) and move toward the positive electrode (10) or the negative electrode (20).

[0024] positive electrode (10)

[0025] A 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) may include a positive electrode active material and may further include a binder and / or a conductive material.

[0026] For example, the anode (10) may further include an additive that can serve as a sacrificial anode.

[0027] The content of the positive active material in the positive active material layer (AML1) may be 90% to 99.5% by weight with respect to 100% by weight of the positive active material layer (AML1). The content of the binder and the conductive material may each be 0.5% to 5% by weight with respect to 100% by weight of the positive active material layer (AML1).

[0028] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector (COL1). Representative 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)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0029] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0030] Al can be used as the current collector (COL1), but is not limited thereto.

[0032] positive electrode active material

[0033] As the positive active material in the positive active material layer (AML1), a compound capable of reversible intercalation and deintercalation of lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0034] The above composite oxide may be a lithium transition metal composite oxide, and specific examples include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0035] As an example, a compound represented by any one of the following chemical formulas may 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); 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 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 aNiG 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).

[0036] 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; L 1 is Mn, Al, or a combination thereof.

[0037] For example, the above-mentioned positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide 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. The high-nickel positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0039] Negative electrode (20)

[0040] A negative electrode (20) for a lithium secondary battery comprises 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) comprises a negative electrode active material and may further comprise a binder and / or a conductive material.

[0041] 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.

[0042] The above binder serves to effectively bond the negative electrode active material particles to each other and also to effectively bond the negative electrode active material to the current collector (COL2). As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof may be used.

[0043] Examples of the above-mentioned 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.

[0044] The above-mentioned water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0045] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0046] The above dry binder is a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0047] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0048] 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, and combinations thereof may be used.

[0050] cathode active material

[0051] The negative electrode active material in the negative electrode active material layer (AML2) comprises a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0052] A material capable of reversibly intercalating / deintercalating the above lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0053] As the above lithium metal alloy, 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 may be used.

[0054] As a material capable of doping and undoping the above lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may be silicon, a silicon-carbon composite, SiOx (0 < x < 2), a Si-Q alloy (wherein 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 may be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0055] The silicon-carbon composite may 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 a secondary particle (core) assembled from silicon primary particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particle. The amorphous carbon may also be located between the silicon primary particles, so that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0056] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0057] The above Si-based or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0059] Separator (30)

[0060] Depending on the type of lithium secondary battery, a separator (30) may be present between the positive electrode (10) and the negative electrode (20). As such a separator (30), polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and of course, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0061] The separator (30) may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0062] The porous substrate may be a polymer membrane formed from any one of the following: polyolefins such as polyethylene and 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 a copolymer or mixture of two or more of these.

[0063] The above organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0064] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include, but is not limited to, inorganic particles selected from SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0065] The above organic and inorganic materials may exist mixed in a single coating layer, or may exist in a stacked form with a coating layer containing organic materials and a coating layer containing inorganic materials.

[0067] Electrolyte (ELL)

[0068] The electrolyte (ELL) for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0069] The above-mentioned non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0070] The above-mentioned non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0071] The above carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc.

[0072] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0073] As ether-based solvents, dibutyl ether, tetraglame, diglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Additionally, 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 straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. may be used.

[0074] The above-mentioned non-aqueous organic solvent can be used alone or in a mixture of two or more types.

[0075] In addition, when using a carbonate-based solvent, a mixture of cyclic carbonates and chain carbonates can be used, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0076] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and facilitating the movement of lithium ions between the anode and cathode. Representative 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, LiN(C x F 2x+1 SO2)(C y F 2y+1 It may include one or more selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0078] lithium secondary battery

[0079] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, coin, etc., depending on their shape. FIGS. 2 to 5 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, where FIG. 2 is a cylindrical battery, FIG. 3 is a prismatic battery, and FIGS. 4 and 5 are pouch-type batteries. Referring to FIGS. 2 to 4, the lithium secondary battery (100) may include an electrode assembly (40) having 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), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as in FIG. 2. In addition, in FIG. 3, the lithium secondary battery (100) may include a positive lead tab (11) and a positive terminal (12), a negative lead tab (21) and a negative terminal (22). As shown in FIG. 4 and FIG. 5, the lithium secondary battery (100) may include electrode tabs (70), namely a positive tab (71) and a negative tab (72), which serve as electrical passages for inducing current formed in the electrode assembly (40) to the outside.

[0080] Hereinafter, a lithium secondary battery according to embodiments of the present invention will be described in more detail.

[0081] FIG. 6 is a cross-sectional view showing a lithium secondary battery according to embodiments of the present invention. FIG. 7 is an enlarged cross-sectional view of region M of FIG. 6.

[0082] Referring to FIG. 6, as previously described with reference to FIG. 1, the lithium secondary battery according to the present invention may include a positive electrode (10), a negative electrode (20), and a separator (30) between the positive electrode (10) and the negative electrode (20). Although not explicitly shown in FIG. 6, the lithium secondary battery according to the present invention may further include an electrolyte (ELL). The separator (30) may be impregnated with the electrolyte (ELL).

[0083] The positive electrode (10) may include a positive current collector (COL1) and a positive active material layer (AML1) on the positive current collector (COL1). The negative electrode (20) may include a negative current collector (COL2) and a negative active material layer (AML2) on the negative current collector (COL2). A separator (30) may be interposed between the positive active material layer (AML1) and the negative active material layer (AML2).

[0084] Referring to FIG. 7, the negative active material layer (AML2) may include a plurality of negative patterns (NPT) formed on its upper surface. Each of the plurality of negative patterns (NPT) may extend from the upper surface of the negative active material layer (AML2) toward the lower surface of the negative active material layer (AML2). The upper surface of the negative active material layer (AML2) may be adjacent to or in contact with the separator (30). In other words, the plurality of negative patterns (NPT) may be adjacent to the separator (30). The electrolyte (ELL) may fill the plurality of negative patterns (NPT).

[0085] The cathode active material layer (AML2) may include a plurality of photoresist particles (PRP) formed on its upper surface. The plurality of photoresist particles (PRP) may be provided on the surface of the intaglio pattern (NPT) and the surface of the non-intaglio pattern (UPT), respectively.

[0086] According to one embodiment of the present invention, photoresist particles (PRP) may include a photosensitive resin and a photo-generating agent, and a specific description thereof is provided below in the photoresist composition.

[0087] Referring again to FIG. 7, the maximum depth (d) of the intaglio pattern may be smaller than the thickness (D) of the negative electrode active material layer. Specifically, the ratio (d / D) of the maximum depth (d) of the intaglio pattern to the thickness (D) of the negative electrode active material layer may be greater than 0 and less than or equal to 0.1.

[0088] Referring again to FIG. 7, the amount of photoresist particles (PRP) located on the surface of the intaglio pattern (NPT) may be greater than the amount of photoresist particles (PRP) located on the surface of the non-intaglio pattern (UPT). This can be confirmed through SEM cross-sectional analysis, specifically by taking a sample of an area (1 cm²) with a width of 1 cm and a length of 1 cm in the cathode active material layer (AML2).

[0089] In one embodiment, the density of photoresist particles (PRP) of an intaglio pattern (NPT) may be greater than the density of photoresist particles (PRP) of a non-intaglio pattern (UPT). In this specification, the “density of photoresist particles” refers to the density of a unit area (e.g., 10,000 μm) of the cathode active material layer (AML2) in a cross-sectional image of the cathode active material layer (AML2) such as FIG. 7. 2 It can be defined as the ratio of the area occupied by photoresist particles (PRP) within a width of 100㎛ x a height of 100㎛.

[0090] Specifically, a prepared sample of 1 cm² can be fixed to an SEM stage, and a cross-sectional image can be obtained by taking a SEM image. After loading the image using an image analysis tool (e.g., MATLAB, ImageJ, etc.), a binary thresholding process can be performed to separate photoresist particles (PRP) and the cathode active material layer (AML2) based on brightness contrast. After converting the image separated through binary thresholding into a black region representing the cathode active material layer and a white region representing the photoresist particles by setting an appropriate threshold, the density of the photoresist particles can be calculated using Equation 1 below.

[0091] [Equation 1]

[0092] Forest particle density (%) = (Number of pixels in white areas / Total number of pixels) X 100

[0093] When the density of photoresist particles in the negative pattern (NPT) is greater than the density of photoresist particles in the non-negative pattern (UPT), it improves the imbalance in lithium-ion mobility resistance that may occur between the negative pattern (NPT) and the non-negative pattern (UPT), thereby enabling more stable operation of the lithium secondary battery. Additionally, the presence of photoresist particles within the negative pattern (NPT) strengthens the mechanical strength of the anode, which can prevent damage to the anode.

[0094] FIG. 8 is a plan view of region M of FIG. 6 viewed in the horizontal direction. FIG. 9 is an enlarged plan view of region A of FIG. 8.

[0095] Referring to FIGS. 8 and 9, in this specification, 'unit area (A)' may be defined as an area (1 cm²) with a width of 1 cm and a height of 1 cm within the cathode active material layer (AML2), and “areal density of photoresist particles” may be defined as the area of ​​photoresist particles (PRP) within the unit area (A). Accordingly, the areal density of photoresist particles on the surface of the cathode active material layer (AML) may be greater than 0 and less than or equal to 0.05 cm².

[0096] Specifically, a sample of the prepared unit region (A) is photographed using an optical microscope to observe the regions where photoresist particles (PRP) exist within the surface of the cathode active material layer (AML2). Cross-sectional images are obtained by photographing each of the regions where photoresist particles (PRP) exist using an SEM. After loading the images using an image analysis tool (e.g., MATLAB, ImageJ, etc.), a binary thresholding process can be performed to separate the photoresist particles (PRP) and the cathode active material layer (AML2) based on brightness contrast. After converting the images separated through binary thresholding into black regions representing the cathode active material layer and white regions representing the photoresist particles by setting an appropriate threshold, the area density of the photoresist particles can be obtained by calculating the sum of the areas occupied by the white regions in each image.

[0097] When the areal density of the photoresist particles is greater than 0 and less than or equal to 0.05 cm², the movement of lithium ions from the negative electrode surface is not hindered, and the detachment of the electrode plate during the intaglio pattern processing and charging / discharging process is prevented, allowing the lithium secondary battery to operate stably. On the other hand, when the areal density of the photoresist particles exceeds 0.05 cm², the movement of lithium from the negative electrode surface is hindered, which increases the lithium ion mobility resistance and simultaneously degrades the rate capability of the lithium secondary battery.

[0098] FIG. 10 is an enlarged view of a triangular shape, which is one embodiment of an intaglio pattern that can be formed on the negative electrode active material layer (AML2) of the present invention. FIG. 11 is an enlarged view of a multi-hole shape, which is another embodiment of an intaglio pattern that can be formed on the active material layer of the present invention.

[0099] Referring to FIG. 11, the multi-hole shape in this specification may refer to a polyhedron shape composed of various polygons, rather than a simple shape such as a triangular shape. In one embodiment, the multi-hole shape may be a fractal shape having self-similarity, in which the overall structure and a part of the structure repeatedly exhibit the same or similar patterns.

[0100] For example, the multi-hole shape may include a first triangular shape (1T) and a second triangular shape (2T) on one side of the first triangular shape (1T). The size of the second triangular shape (2T) may be smaller than the size of the first triangular shape. By forming the multi-hole shape, the resistance to movement of lithium ions at the interface of the negative electrode active material layer can be reduced and ion conductivity can be improved.

[0101] FIGS. 12 and FIGS. 13 are cross-sectional views illustrating the process of manufacturing a cathode according to one embodiment of the present invention.

[0102] Referring to FIGS. 12 and 13, a negative active material layer (AML2) can be formed on a negative current collector (COL2). Additionally, a photoresist layer (PRL) can be formed on the negative active material layer (AML2). At this time, forming the negative active material layer (AML2) and the photoresist layer (PRL) can be performed by a coating method. By forming the photoresist layer (PRL) on the negative active material layer (AML2), the photoresist layer (PRL) suppresses the detachment of the negative active material during the intaglio pattern processing process and further serves as a protective layer that minimizes damage to the negative electrode.

[0103] FIG. 14 is a conceptual diagram illustrating a method for manufacturing an electrode for a lithium secondary battery, comprising a process of forming an intaglio pattern (NPT) on a negative electrode active material layer (AML2) according to one embodiment of the present invention. FIG. 15 is a cross-sectional view illustrating a method for manufacturing an electrode for a lithium secondary battery, comprising a process of forming an intaglio pattern (NPT) on a negative electrode active material layer (AML2) by a roll press method according to one embodiment of the present invention.

[0104] Referring to FIGS. 14 and 15, an intaglio pattern processing process can be performed on the cathode active material layer (AML2). A plurality of intaglio patterns (NPT) can be formed on the photoresist layer (PRL) and the cathode active material layer (AML2). In one embodiment, the intaglio pattern processing process can be performed by a presser having a plurality of relief patterns formed thereon. More specifically, the intaglio pattern processing process can be performed by a roll press method. A relief pattern may be formed on the upper roll. A relief pattern may not be formed on the lower roll.

[0105] Referring to FIG. 15, the thickness (P) of the photoresist layer can be formed such that the ratio (d / P) of the maximum depth (d) of the intaglio pattern to the thickness (P) of the photoresist layer is greater than 0 and less than or equal to 1. When the ratio (d / P) of the maximum depth (d) of the intaglio pattern to the thickness (D) of the photoresist layer is greater than 0 and less than or equal to 1, the photoresist layer (PRL) can serve as a protective layer that suppresses the detachment of the cathode active material during the intaglio pattern processing process. When the ratio (d / P) of the maximum depth (d) of the intaglio pattern to the thickness (P) of the photoresist layer exceeds 1, when the embossed pattern formed according to one embodiment of the present invention is pressed by a pressurizer, the embossed pattern comes into direct contact with the cathode active material layer (AML2), which may cause the detachment of the active material and damage to the cathode.

[0106] Referring to FIG. 14, a photoresist layer (PRL) having an intaglio pattern (NPT) formed thereon can be selectively removed through an exposure process. At this time, the wavelength of the irradiated light can be varied depending on the type of photoresist composition used.

[0107] Referring to FIGS. 13 and 14, the photoresist composition according to embodiments of the present invention may be a chemically amplified (CAR type) photoresist composition.

[0108] The photoresist composition of the present invention may include a photoresist resin, a photo-acid generator (PAG), an additive, and a solvent.

[0109] For example, a photosensitive resin may include a polymer represented by the following chemical formula 1A.

[0110] [Chemical Formula 1A]

[0111]

[0112] In Chemical Formula 1A, R6 may be hydrogen or an alkyl group having 1 to 15 carbon atoms. n may be an integer between 10 and 1,000,000.

[0113] As another example, photosensitive resins may include a polymer represented by the chemical formula 1B below.

[0114] [Chemical Formula 1B]

[0115]

[0116] In chemical formula 1B, R6 may be hydrogen or an alkyl group having 1 to 15 carbon atoms. m may be an integer between 10 and 1,000,000.

[0117] As another example, the photosensitive resin may include a block copolymer represented by the chemical formula 1C below.

[0118] [Chemical Formula 1C]

[0119]

[0120] In chemical formula 1C, R6 and R7 may each independently be hydrogen or an alkyl group having 1 to 15 carbon atoms. n and m may each be an integer between 10 and 1,000,000.

[0121] A photosensitive resin according to one embodiment of the present invention may include a block copolymer represented by the following chemical formula 1D.

[0122] [Chemical Formula 1D]

[0123]

[0124] In chemical formula 1D, n and m can each be integers between 10 and 1000000.

[0125] Photogenerators may include substances capable of generating acid by light of a specific wavelength.

[0126] The solvent may comprise at least one selected from the group consisting of ethyl cellosolve acetate (ECA), ethyl lactate (EL), propylene glycol monomethyl ether acetate (PGMEA), propylene glycol methyl ether (PGME), N-butyl acetate (n-BA), 2-heptanone (MAK), methyl ethyl ketone (MEK), N,N-Dimethyl formamide (DMF), N-Methylpyrrolidone (NMP), ethyl 3-ethoxypropionate (EEP), methyl 3-methoxypropionate (MMP), ethyl pyruvate (EP), and isopropyl alcohol (IPA).

[0127] The photoresist composition may be used without limitation as used in general semiconductor processes, and the above description is merely one example and is not particularly limited thereto.

[0128] After performing the intaglio pattern processing process, a slitting process and a notching process can be sequentially performed on the negative electrode (20). A lithium secondary battery according to the present invention can be manufactured by stacking the negative electrode (20), separator (30), and positive electrode (10) and providing an electrolyte (ELL).

[0129] The following describes embodiments and comparative examples of the present invention. However, the following embodiments are merely examples of the present invention, and the present invention is not limited to the following embodiments.

[0131] Example 1

[0132] (Manufacturing of the cathode)

[0133] A Cu foil with a thickness of 10 μm was prepared as a negative electrode current collector. Artificial graphite, styrene-butadiene rubber binder, and carboxymethylcellulose were mixed in a weight ratio of 98:1:1, respectively, and dispersed in distilled water to prepare a negative electrode active material slurry. The negative electrode active material slurry was coated onto a current collector with a thickness of 10 μm and dried at 100°C to form a negative electrode active material layer.

[0134] A photoresist layer was formed by coating a chemically amplified positive photoresist composition, comprising a mixture of a photosensitive resin (poly(hydroxystyrene)), a photogenerative agent (triphenylsulfonium triflate), a solvent (PGMEA), and an additive (surfactant), onto a cathode active material layer.

[0135] A roll press process was performed on a photoresist layer using a roll having a triangular embossed pattern formed thereon. This formed a plurality of triangular intaglio patterns on the upper surface of the cathode active material layer. At this time, the intaglio patterns were formed such that the ratio (d / D) of the maximum depth (d) of the intaglio pattern to the thickness (D) of the cathode active material layer was 0.1. Additionally, the intaglio patterns were formed such that the ratio (d / P) of the maximum depth (d) of the intaglio pattern to the thickness (P) of the photoresist layer was 1.

[0136] The photoresist layer was removed by performing an exposure process on the front surface of the remaining photoresist layer. Thus, the cathode according to the present embodiment was manufactured.

[0138] (2) Manufacturing of lithium secondary batteries

[0139] An Al foil with a thickness of 15 μm was prepared as a positive current collector. NCA (LiNiCoAlO2) as the positive active material, polyvinylidene fluoride as the binder, and acetylene black as the conductive material were mixed in a weight ratio of 96:3:1, respectively, and dispersed in N-methylpyrrolidone to prepare a positive active material slurry.

[0140] The above positive active material slurry was coated onto a current collector with a thickness of 15 μm, dried at 100°C, and then pressed to manufacture a positive electrode.

[0141] An electrode assembly was manufactured by assembling the above positive electrode and the above negative electrode with a separator made of polyethylene material with a thickness of 10 μm, and a lithium secondary battery was manufactured by injecting the above electrolyte.

[0143] Example 2

[0144] In the process of processing an intaglio pattern, the embossed pattern of the upper roll included a first triangular shape and a second triangular shape on one side of the first triangular shape. The embossed pattern has a fractal shape in which the size of the second triangular shape is smaller than the size of the first triangular shape. An intaglio pattern having a multi-hole shape was formed by performing a roll press process with the upper roll. A lithium secondary battery was manufactured in the same manner as in Example 1.

[0146] Comparative Example 1

[0147] A lithium secondary battery was manufactured using the same method as in Example 1, except that a photoresist composition was not coated so that a photoresist layer was not formed, and an intaglio pattern was not formed on the negative active material layer by applying pressure with an upper roll without an embossed pattern.

[0149] Comparative Example 2

[0150] A lithium secondary battery was manufactured using the same method as in Example 1, except that the photoresist composition was not coated so that a photoresist layer was not formed.

[0152] Evaluation Example 1: Evaluation of active material shedding rate after press process

[0153] According to Examples 1 and 2 and Comparative Examples 1 and 2, the rate of active material detachment was evaluated by comparing the measured Loading Level with the designed Loading Level after performing intaglio pattern processing and press processes. Ten samples were measured for each example and comparative example, and the average value was used as the Loading Level (measured) and is shown in Table 1 below.

[0154] division Loading Level (Design) (mg / cm²) Loading Level (Measurement) (mg / cm²) Amount of active material shed (mg / cm²) Active material shedding rate (%) Example 1 15.00 14.77 0.23 1.5 Example 2 15.00 14.60 0.40 2.7 Comparative Example 1 15.00 14.97 0.03 0.2 Comparative Example 2 15.00 14.10 0.90 6.0

[0155] Referring to Table 1, it can be seen that in Comparative Example 1, in which no intaglio pattern is formed, the active material detachment rate is significantly lower compared to Examples 1 and 2 and Comparative Example 2, in which an intaglio pattern is formed. Additionally, in the case of Example 2, in which a fractal-shaped intaglio pattern is formed, the active material detachment rate is higher compared to Example 1, in which a triangular-shaped intaglio pattern is formed; however, it can be seen that the active material detachment rate is significantly lower when compared to Comparative Example 2, in which a triangular-shaped intaglio pattern is formed for both Examples 1 and 2 but no photoresist layer is formed.

[0156] In conclusion, while the rate of active material detachment increases as the complex engraving pattern is formed, it can be confirmed that the rate of active material detachment can be significantly reduced when a photoresist layer is present during the engraving pattern processing process.

[0158] Evaluation Example 2: Evaluation of Lithium Ion Migration Resistance

[0159] The lithium secondary batteries prepared according to the examples and comparative examples were discharged at 1C from a fully charged state (100% SOC). 1C discharge means discharging the battery capacity within one hour, and for example, a 2Ah capacity battery is discharged at a current of 2A for one hour.

[0160] Using EIS equipment, a frequency range from 10 mHz to 1 Hz was set, and the impedance was measured and visualized in the form of a Nyquist Plot. The actual impedance value where the semicircle formed intersects the X-axis on the Nyquist Plot was extracted to measure the lithium ion mobility resistance, and the results are shown in Table 2 below.

[0162] Evaluation Example 3: Evaluation of Dose Retention Rate

[0163] The lithium secondary batteries prepared according to the examples and comparative examples were charged to a full charge state (100% SOC), and the capacity retention rate was evaluated by repeating discharge and charge 100 times with a constant current of 1C using Equation 2 below. A lower capacity retention rate indicates that the electrode interface structure is unstable and mechanical damage to the electrode has occurred. The results of the evaluation are shown in Table 2 below.

[0164] [Equation 2]

[0165] Capacity retention rate (%) = (Capacity after discharge / Initial capacity) X 100

[0167] Evaluation Example 4: Evaluation of Initial Charge / Discharge Efficiency

[0168] The first coulombic efficiency (FCE) of the lithium secondary batteries prepared according to the examples and comparative examples was evaluated by the following charge-discharge test. The charge-discharge test used the CC-CV method. The battery was charged at a constant current of 1C until the battery voltage reached 4.2V from a fully discharged state, and upon reaching 4.2V, the first charge was performed at a constant voltage of 4.25V with a 0.05C cut-off condition. Subsequently, the first discharge was performed at a constant current of 0.1C until the battery voltage reached 2.75V, thereby completing the first charge-discharge cycle. Afterward, the first charge-discharge efficiency was measured according to Equation 3 below, and the results are shown in Table 2 below. A higher first charge-discharge efficiency indicates superior electrode structure and electrode interface stability.

[0169] [Equation 3]

[0170] Initial charge / discharge efficiency (%) = (Discharge capacity of the first charge / discharge cycle / Charge capacity of the first charge / discharge cycle) X 100

[0172] division Li + Moving resistance (Ω·cm²) Capacity retention rate (%) Initial charge / discharge efficiency (%) Example 1 15.52 89.8 91.9 Example 2 12.74 88.7 90.7 Comparative Example 1 21.13 92.2 94.1 Comparative Example 2 14.12 82.1 86.6

[0173] Referring to Table 2, it can be seen that in the case of Examples 1 and 2 and Comparative Example 2, in which an intaglio pattern is formed on the surface of the negative electrode active material layer, the lithium ion mobility resistance is lower than that of Comparative Example 1 (21.13 Ω·cm²), in which no intaglio pattern is formed. Specifically, it can be seen that Comparative Example 2 (14.12 Ω·cm²), in which photoresist particles are absent, is lower than that of Example 1 (15.52 Ω·cm²) and Example 2 (12.74 Ω·cm²), in which photoresist particles are present, and it can be seen that the lithium ion mobility resistance of Example 2, in which a fractal intaglio pattern is formed, is lower than that of Example 1, in which a triangular intaglio pattern is formed.

[0174] In conclusion, it can be confirmed that the mobility resistance of lithium ions decreases as complex engraving patterns are formed, and increases when photoresist particles are present on the surface of the negative electrode active material layer.

[0175] Referring again to Table 2, it can be seen that the capacity retention rate and initial charge / discharge efficiency of Examples 1 and 2 and Comparative Example 2, in which an intaglio pattern is formed, are lower than those of Comparative Example 1, in which no intaglio pattern is formed. Specifically, it can be seen that Comparative Example 2, in which the intaglio pattern processing process was performed without forming a photoresist layer, has a lower capacity retention rate and initial charge / discharge efficiency than Examples 1 and 2, in which the intaglio pattern processing process was performed after the photoresist layer was formed. Additionally, it can be seen that Example 2, in which a fractal-shaped intaglio pattern is formed, has a lower capacity retention rate and initial charge / discharge efficiency than Example 1, in which a triangular-shaped intaglio pattern is formed.

[0176] In conclusion, it can be confirmed that capacity retention rate and initial charge / discharge efficiency increase as the structural stability of the cathode surface increases (e.g., as the active material shedding rate decreases).

[0178] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention. Explanation of the symbols

[0180] 100: Lithium secondary battery 10: Positive electrode 11: Positive lead tab 12: Positive terminal 20: Cathode 21: Cathode lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode tab 71: Positive tab 72: Negative tab

Claims

Claim 1 A method for manufacturing a negative electrode for a lithium secondary battery, comprising: forming a negative electrode active material layer on a negative electrode current collector; forming a photoresist layer on the negative electrode active material layer; performing an intaglio pattern processing process on the photoresist layer to form an intaglio pattern on the negative electrode active material layer; and selectively removing the photoresist layer. Claim 2 A method for manufacturing a negative electrode for a lithium secondary battery, wherein, in claim 1, the forming of the intaglio pattern is performed by a roll press. Claim 3 A method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, wherein forming the photoresist layer comprises coating a photoresist composition, and the photoresist composition comprises a photosensitive resin, a photogenerative agent, a matting agent, an additive, and a solvent. Claim 4 A method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, wherein the ratio (d / P) of the maximum depth (d) of the intaglio pattern to the thickness (P) of the photoresist layer is greater than 0 and less than or equal to 1. Claim 5 A method for manufacturing a negative electrode for a lithium secondary battery, wherein, in claim 1, the intaglio pattern has a triangular shape. Claim 6 A method for manufacturing a negative electrode for a lithium secondary battery, wherein, in claim 1, the intaglio pattern has a multi-hole shape. Claim 7 A method for manufacturing a negative electrode for a lithium secondary battery according to claim 6, wherein the multi-hole shape comprises a first triangular shape; and the first triangular shape comprises a second triangular shape on one side, and the size of the second triangular shape is smaller than the size of the first triangular shape. Claim 8 A negative electrode for a lithium secondary battery comprising: a negative current collector; a negative active material layer on the negative current collector; and photoresist particles on the surface of the negative active material layer, wherein the negative active material layer comprises an intaglio pattern formed on the upper surface of the negative active material layer. Claim 9 A negative electrode for a lithium secondary battery according to claim 8, wherein the areal density of the photoresist particles on the surface of the negative electrode active material layer is greater than 0 and less than or equal to 0.

05. Claim 10 In claim 8, the photoresist particles comprise a positive-type photoresist material, and the positive-type photoresist material comprises a polymer resin and a photosensitive agent, a negative electrode for a lithium secondary battery. Claim 11 A negative electrode for a lithium secondary battery according to claim 8, wherein the negative electrode active material layer comprises an intaglio pattern and a non-intaglio pattern, the photoresist particles comprise a plurality of photoresist particles, and the plurality of photoresist particles are provided on the surface of the intaglio pattern and the surface of the non-intaglio pattern. Claim 12 A negative electrode for a lithium secondary battery according to claim 8, wherein the density of the photoresist particles on the surface of the intaglio pattern is greater than the density of the photoresist particles on the surface of the non-intaglio pattern. Claim 13 A negative electrode for a lithium secondary battery according to claim 8, wherein the ratio (d / D) of the maximum depth (d) of the intaglio pattern to the thickness (D) of the active material layer is greater than 0 and less than or equal to 0.

1. Claim 14 In claim 8, the above-mentioned intaglio pattern is a negative electrode for a lithium secondary battery having a triangular shape. Claim 15 In claim 8, the above-mentioned intaglio pattern is a negative electrode for a lithium secondary battery having a multi-hole shape. Claim 16 A negative electrode for a lithium secondary battery according to claim 15, wherein the multi-hole shape comprises a first triangular shape; and the first triangular shape comprises a second triangular shape on one side, wherein the size of the second triangular shape is smaller than the size of the first triangular shape. Claim 17 A lithium secondary battery comprising: a positive electrode; a negative electrode according to claim 8; and a separator between the positive electrode and the negative electrode. Claim 18 In claim 17, the intaglio pattern formed on the upper part of the above-mentioned negative electrode is a lithium secondary battery adjacent to the above-mentioned separator. Claim 19 In claim 17, the above-mentioned positive electrode is a lithium secondary battery in which the positive electrode active material comprises a lithium transition metal composite oxide. Claim 20 A lithium secondary battery comprising a liquid electrolyte in Clause 17.

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