Positive electrode and lithium secondary battery containing the same

Abstract

To provide a positive electrode that facilitates electrode plate manufacturing by increasing the bonding force between the current collector and the positive electrode active material. Furthermore, to provide a positive electrode with improved capacitance characteristics and lifespan characteristics. [Solution] The present invention relates to a positive electrode and a lithium secondary battery containing the same, and more particularly to a current collector, a first active material layer on the current collector, and a second active material layer on the first active material layer, wherein the first active material layer comprises first particles containing a layered positive electrode active material, second particles containing an olivine-based positive electrode active material, a first conductive material, and a first binder, and the second active material layer comprises the second particles, a second conductive material, and a second binder, wherein the content of the first particles in the first active material layer is 70% or more and 90% or less.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode and a lithium secondary battery containing the same, and more particularly to a positive electrode containing a Ni-based active material and a lithium secondary battery containing the same. [Background technology]

[0002] Recently, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptops, and electric vehicles, the demand for rechargeable batteries with high energy density and high capacity has been rapidly increasing. Therefore, research and development to improve the performance of lithium-ion rechargeable batteries is being actively pursued.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode containing an active material capable of intercalation and deintercalation of lithium ions, and an electrolyte. It produces electrical energy through oxidation and reduction reactions that occur when lithium ions are intercalated / deintercalated at the positive and negative electrodes. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Korean Published Patent Publication No. 2023-0146887 [Patent Document 2] Korean Published Patent No. 2023-0162454 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The problem that this invention aims to solve is to provide a positive electrode that facilitates electrode plate manufacturing by increasing the bonding force between the current collector and the positive electrode active material.

[0006] Another problem that the present invention aims to solve is to provide a positive electrode with improved capacitance characteristics and lifetime characteristics. [Means for solving the problem]

[0007] A positive electrode for a lithium secondary battery according to one embodiment of the present invention includes a current collector, a first active material layer on the current collector, and a second active material layer on the first active material layer, wherein the first active material layer includes first particles containing a nickel-based active material, second particles containing lithium, a first conductive material, and a first binder, and the second active material layer includes the second particles, a second conductive material, and a second binder, and the content of the first particles in the first active material layer may be 70% or more and 90% or less.

[0008] A positive electrode for a lithium secondary battery according to another concept of the present invention comprises a current collector, a first active material layer on the current collector, and a second active material layer on the first active material layer, wherein the first active material layer comprises first particles, second particles, a first conductive material, and a first binder, and the second active material layer comprises the second particles, a second conductive material, and a second binder, wherein the first particles comprise a nickel-based active material, and the second particles comprise Li, Fe, and PO4, and the weight of the first particles may be 25% to 35% of the total weight of the first and second active material layers.

[0009] A lithium secondary battery according to one embodiment of the present invention may include the above-described positive electrode. [Effects of the Invention]

[0010] The positive electrode according to the present invention can improve battery characteristics by including a double-layer active material layer with different ratios of Ni-based active material.

[0011] The positive electrode according to the present invention can reduce battery resistance by including an active material layer with a high ratio of Ni-based active material. [Brief explanation of the drawing]

[0012] [Figure 1] This is a simplified conceptual diagram showing a lithium secondary battery according to an embodiment of the present invention. [Figure 2] This is a schematic diagram showing a lithium secondary battery according to one embodiment, which has a cylindrical battery shape. [Figure 3] It is a cross-sectional view showing a lithium secondary battery according to an embodiment. [Figure 4] It is a schematic view showing a lithium secondary battery according to an embodiment, and has a rectangular battery form. [Figure 5] It is a schematic view showing a lithium secondary battery according to an embodiment, and has a pouch-shaped battery form. [Figure 6] It is a cross-sectional view of a positive electrode for a secondary battery according to an embodiment of the present invention. [Figure 7] It is an enlarged view of a first active material layer according to an embodiment of the present invention. [Figure 8] It is an enlarged view of a second active material layer according to an embodiment of the present invention. [Figure 9] It is an enlarged view of a first active material layer according to an embodiment of the present invention. [Figure 10] It is an enlarged view of a second active material layer according to an embodiment of the present invention. [Figure 11] It is an enlarged view of a second active material layer according to an embodiment of the present invention. [Figure 12] It is a graph for explaining the adhesive force of a battery according to an embodiment of the present invention. [Figure 13] It is a graph for explaining the resistance of a battery according to an embodiment of the present invention. [Figure 14] It is a drawing for explaining a method of manufacturing a positive electrode according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0013] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be realized in various forms and various modifications can be made. It is merely provided so that the disclosure of the present invention becomes complete through the description of the present embodiment and so that those having ordinary knowledge in the technical field to which the present invention pertains can fully know the scope of the invention.

[0014] Where a given component is referred to as being on top of another component, it means that it may be formed directly on top of 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.

[0015] 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.

[0016] Unless otherwise specified herein, singular nouns may also include plural nouns. Furthermore, unless otherwise specified herein, “A or B” may mean “including A, including B, or including A and B.” The terms “comprises” and / or “comprising” used in this specification do not preclude the presence or addition of one or more other components.

[0017] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0018] In this specification, a single particle means a particle that does not have a grain boundary within it, exists independently, and consists of one particle. It can mean a single particle, monolithic structure, or non-aggregated particle that exists in an independent phase where particles do not aggregate morphologically, and one example is a single crystal. Alternatively, a single particle may be a particle containing several crystals. The single particle may exist in a form that is separated individually, or in a form in which fewer than 10 single particles are attached to each other.

[0019] 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.

[0020] 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 immersed in the electrolyte ELL.

[0021] 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, the lithium ions can move towards the positive electrode 10 or the negative electrode 20 by passing through the separator 30.

[0022] 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.

[0023] As an example, the positive electrode 10 may further contain an additive that can act as a sacrificial positive electrode.

[0024] Al can be used as the current collector COL1, but it is not limited to this.

[0025] The positive electrode 10 according to the embodiment of the present invention will be described later with reference to Figure 6.

[0026] 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.

[0027] 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.

[0028] 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. The binder can be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0029] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0030] 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.

[0031] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li.

[0032] The dry binder may 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.

[0033] The conductive material is used to impart conductivity to the 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 powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0034] As the current collector COL2, those selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be used.

[0035] 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.

[0036] Examples of the material capable of reversibly intercalating / deintercalating the lithium ions include, as a carbon-based negative electrode active material, crystalline carbon, amorphous carbon, or combinations thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, etc.

[0037] As the alloy of the 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.

[0038] 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 combinations thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or combinations thereof.

[0039] 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 coating 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. The 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 the amorphous carbon matrix.

[0040] 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.

[0041] The Si-based or Sn-based anode active material can be used in combination with a carbon-based anode active material.

[0042] 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 can 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.

[0043] 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.

[0044] The porous substrate may be a polymer film formed from any 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, and polytetrafluoroethylene (e.g., Teflon®), or from two or more copolymers or mixtures thereof.

[0045] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0046] The inorganic material may include, but is not limited to, Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and inorganic particles selected from combinations thereof.

[0047] The organic and inorganic materials may exist mixed together in a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are laminated together.

[0048] Electrolyte ELL The ELL electrolyte for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0049] The aforementioned non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0050] The 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.

[0051] 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).

[0052] Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0053] As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. As ketone-based solvents, cyclohexanone, etc. can be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. can be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 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; sulfolanes, etc. can be used.

[0054] The aforementioned non-aqueous organic solvents can be used alone or in combination of two or more.

[0055] 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.

[0056] The aforementioned lithium salts dissolve in organic solvents and act as a source of lithium ions within the battery, enabling the basic operation of lithium secondary batteries and promoting 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 It may include one or more selected from SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0057] 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 cylindrical, Figure 3 is prismatic, and Figures 4 and 5 are pouch-shaped. Referring to Figures 2 to 4, the lithium secondary battery 100 may 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 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 shown in Figure 2. Also, in Figure 3, the lithium secondary battery 100 may 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.

[0058] A lithium secondary battery according to one embodiment of the present invention can be applied to automobiles, mobile phones, and / or various forms of electrical devices, but the present invention is not limited thereto.

[0059] The positive electrode of the double-layer structure of the first particle PTC1 and the second particle PTC2 will be described in more detail below.

[0060] 1st particle PTC1 The first particle PTC1 may contain a layered cathode active material.

[0061] In one embodiment, the layered cathode active material may include nickel (Ni). Specifically, the layered cathode active material may include at least one selected from the group consisting of lithium nickel oxide (LNO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt manganese aluminum oxide (NCMA).

[0062] As one embodiment, the first particle PTC1 can contain a compound represented by the following Chemical Formula 1: [Chemical Formula 1] Li a1 Ni x1 Co y1 Mn z1 X c1 O 2-b1 In Chemical Formula 1, 0.8 ≦ a1 ≦ 1.2, 0.8 ≦ x1 ≦ 1.0, 0 ≦ y1 ≦ 0.2, 0 ≦ z1 ≦ 0.2, 0 ≦ c1 ≦ 0.05, and 0 ≦ b1 ≦ 0.05 may hold.

[0063] In Chemical Formula 1, x1 + y1 + z1 + c1 ≦ 1 may hold. As an example, x1 + y1 + z1 + c1 = 1 may hold.

[0064] In Chemical Formula 1, X may be Al, Ti, Mg, Zr, Mo, or Nb.

[0065] The first particle PTC1 has the advantages of high capacity and high energy density. As an example, the first particle PTC1 is a high-nickel-based cathode active material containing a high content of nickel and can achieve high capacity and high performance.

[0066] As one embodiment, the first particle PTC1 can include a first coating layer on its surface. By including the first coating layer, the first particle PTC1 can effectively suppress the structural collapse due to repeated charge and discharge. Therefore, the life characteristics of the secondary battery can be improved.

[0067] The first coating layer may contain aluminum-containing compounds, titanium-containing compounds, magnesium-containing compounds, zirconium-containing compounds, molybdenum-containing compounds, niobium-containing compounds, or combinations thereof. The metal-containing compound in the first coating layer may be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a compound thereof, or a mixture thereof. The metal-containing compound may further contain other metals or nonmetallic elements. For example, the first coating layer may further contain lithium, manganese, and / or nickel, etc.

[0068] The first particle PTC1 may be in the form of a single particle and / or a secondary particle. For example, the first particle PTC1 may be in the form of a primary particle. For example, the first particle PTC1 may exist only as a single particle, only as a secondary particle, or as a mixture of single and secondary particles. In one embodiment, the density can be further improved than when the first particle PTC1 is in a bimodal form, a mixture of single and secondary particle forms.

[0069] As one embodiment, a first particle PTC1 in single-particle form is illustrated with reference to Figures 7 and 8. In this specification, a single particle can mean a single particle that does not have an internal grain boundary. Morphologically, a single particle can mean a single particle, monolithic structure, single-body structure, or non-aggregated particle that exists in independent phases where particles do not aggregate with each other. For example, a single particle may be a single crystal. Or, a single particle may be a particle containing several crystals. A single particle may be in a form that is separated by itself. Or, a single particle may be in a form in which two to 100 single particles are attached to each other. When the first particle PTC1 is a single particle, the average particle size of the first particle PTC1 may be 1 μm to 10 μm.

[0070] In another embodiment, referring to Figures 9 and 10, a secondary particle form of a first particle PTC1 is illustrated. The secondary particle is in a polycrystalline form and means a shape formed by the aggregation of at least two or more secondary primary particles. In other words, one first particle PTC1 can contain a plurality of aggregated primary particles NNP1. The first particle PTC1 can have a spherical or elliptical shape.

[0071] If the first particle is a secondary particle, the average particle size of the first particle PTC1 may be 10 μm to 15 μm. The average particle size of the first particle PTC1 may be the same as, or even larger than, the average particle size of the second particle PTC2, which will be described later. In one embodiment, the average particle size can be measured with a particle size analyzer. The average particle size is determined by arbitrarily selecting about 30 second particles PTC2 from electron microscope images of the positive electrode active material, measuring their particle sizes, and determining the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume. 50 ) can mean.

[0072] 2nd particle PTC2 The second particle PTC2 can contain an olivine-based cathode active material.

[0073] In one embodiment, the olivine-based cathode active material may include at least one selected from the group consisting of lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP).

[0074] In one embodiment, the second particle PTC2 may contain a compound represented by the following chemical formula 2: [C2] Li a2 Fe x2 B y2 PO 4-b2 In the aforementioned chemical formula 2, it is possible that 0.8 ≤ a² ≤ 1.2, 0.1 ≤ x² ≤ 1.0, 0.001 ≤ y² ≤ 0.05, and 0 ≤ b² ≤ 0.05.

[0075] In the aforementioned chemical formula 2, x² + y² ≤ 1 is possible. For example, x² + y² = 1 is possible.

[0076] In the aforementioned chemical formula 2, B may be Ti, Mg, V, or Nb.

[0077] The second particle, PTC2, has advantages such as high cost-effectiveness, high structural stability, and excellent lifetime characteristics. Due to its structural stability, it may undergo relatively little chemical change even after repeated charging and discharging.

[0078] Referring to Figures 7 to 11, the second particle PTC2 can have a primary particle shape. The second particle PTC2 can be a single particle in a primary particle form. In this specification, a single particle can mean a single particle that does not have an internal grain boundary. Morphologically, a single particle can mean a single particle, monolithic structure, single-body structure, or non-aggregated particle that exists in independent phases where particles do not aggregate with each other. As an example, a single particle can be a single crystal. Or, a single particle can be a particle containing several crystals. A single particle can be in a form that is separated by itself. Or, a single particle can be in a form in which two to 100 single particles are attached to each other. When the second particle PTC2 is a single particle, the average particle size of the second particle PTC2 can be 1 μm to 10 μm. The average particle size of the second particle PTC2 can be the same as or smaller than the average particle size of the first particle PTC1 described above. In one embodiment, the average particle size can be measured with a particle size analyzer. The average particle size was determined by randomly selecting approximately 30 secondary particles (PTC2) from electron microscope images of the positive electrode active material and measuring their particle size. The particle size distribution was determined by the diameter (D) of the particle where the cumulative volume was 50%. 50 ) can mean.

[0079] In one embodiment, the second particle PTC2 may have a first coating layer on its surface. The coating layer may cover the entire surface of the second particle PTC2 or a portion of the surface of the second particle PTC2. For example, the coating layer may contain carbon and / or a carbon-containing compound. The second particle PTC2 can have improved structural stability and improved electrical conductivity due to the coating layer.

[0080] First active material layer ATL1 Figure 6 is a cross-sectional view of a positive electrode for a secondary battery according to an embodiment of the present invention. Figure 7 is an enlarged view of the first active material layer ATL1 of a positive electrode for a lithium secondary battery according to an embodiment of the present invention.

[0081] As shown in Figure 6, the first active material layer ATL1 can be placed on the current collector COL1.

[0082] Referring to Figures 7 and 9, the first active material layer ATL1 may include first particles PTC1, second particles PTC2, a first binder BND1, and a first conductive material CDM1.

[0083] The first active material layer ATL1, by containing a mixture of first particles PTC1 and second particles PTC2, can compensate for the disadvantages of lithium iron phosphate-based cathode active materials, namely low capacity and low energy density. In other words, it is possible to simultaneously achieve the advantages of the first particles PTC1, namely high capacity and high energy density, and the advantages of the second particles PTC2, namely economic efficiency.

[0084] The content ratio of the first particle PTC1 in the first active material layer ATL1 may be greater than the content ratio of the first particle PTC1 in the second active material layer ATL2, which will be described later. The content of the first particle PTC1 in the first active material layer ATL1 may be 70% or more and 90% or less. When the content of the first particle PTC1 in the first active material layer ATL1 is 70% or more and 90% or less, the adhesive strength can be improved compared to when the first particle PTC1 is not present or is present at 70% or less, and the electrode plate resistance can be reduced compared to when the first particle PTC1 is present at 90% or more.

[0085] The content of the first binder BND1 may be 1.2 to 2.0 parts by weight per 100 parts by weight of the first active material layer ATL1. The content of the first conductive material CDM1 may be 1.2 to 2.0 parts by weight per 100 parts by weight of the first active material layer ATL1. The content of the first binder BND1 may be less than the content of the second binder BND2, which will be described later. If the first active material layer ATL1 satisfies the conditions for the first binder content range and the first conductive material content range, the capacity and energy density of the battery can be maximized while also achieving ease of electrode plate processing.

[0086] The first binder BND1 plays a role in ensuring good adhesion between the positive electrode active material particles PTC1 and PTC2, and also in ensuring good adhesion between the positive electrode active materials PTC1 and PTC2 and the current collector COL1. Typical examples of the first binder BND1 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.

[0087] The first conductive material CDM1 is used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes can be used in the battery that is constructed. Examples of the first conductive material CDM1 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 powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0088] The first active material layer ATL1 can come into contact with one surface of the current collector COL1 (Figure 6).

[0089] The first active material layer ATL1 may have a thickness T1. In one embodiment, T1 can increase as the weight of the first particles PTC1 and / or second particles PTC2 contained in the first active material layer ATL1 increases.

[0090] Referring again to Figure 7, the first active material layer ATL1 can contain the first particle PTC1 and the second particle PTC2 in the form of single particles. As mentioned above, when the first particle PTC1 is a single particle, the average particle size of the first particle PTC1 can be 1 μm to 10 μm.

[0091] Referring again to Figure 9, the first active material layer ATL1a can contain the second particle PTC2 in the form of a single particle, and the first particle PTC1 can contain the first particle in the form of a secondary particle. The first particle PTC1 may be in the form of a secondary particle formed by the aggregation of nano-sized fine primary particles. In other words, one first particle PTC1 can contain multiple primary particles NNP1 aggregated together. One first particle PTC1 can have a secondary particle shape formed by the aggregation of multiple primary particles NNP1, and the first particle PTC1 can have a spherical or elliptical shape. The average size of the primary particles may be 100 nm to 200 nm. In this case, the average particle size (D) of the first particle 50 ) can be 10 μm to 14 μm.

[0092] Second active material layer ATL2 Figures 8, 10, and 11 are enlarged views of the second active material layer ATL2 of the positive electrode for a lithium secondary battery according to an embodiment of the present invention.

[0093] Figure 8 is an enlarged view when the first particle PTC1 and the second particle PTC2 are in single-particle form. Figure 10 is an enlarged view of the second active material layer ATL2a when the first particle PTC1a is in secondary particle form. Figure 11 is an enlarged view of the second active material layer ATL2b when the first particle PTC1 is absent.

[0094] As shown in Figure 6, the second active material layer ATL2 can be placed on the first active material layer ATL1.

[0095] Referring to Figures 8 and 10, the second active material layer ATL2 may include first particles PTC1, second particles PTC2, second binder BND2, and second conductive material CDM2. Referring to Figure 11, in one embodiment, the second active material layer ATL2 may include second particles PTC2, second binder BND2, and second conductive material CDM2.

[0096] Referring to Figures 8 and 10, the content of the first particles PTC1 and PTCa in the second active material layers ATL2 and ATL2a may be greater than 0 and less than or equal to 30%. Referring to Figure 11, the content of the first particles may be 0.

[0097] The content of first particles PTC1 in the first active material layer ATL1 may be greater than the content of first particles PTC1 in the second active material layer ATL2. In one embodiment, the content of first particles PTC1 in the first active material layer ATL1 may be more than twice the content of first particles PTC1 in the second active material layer ATL2.

[0098] The weight of the first particle PTC1 may be 25% to 35% of the total weight of the first active material layer ATL1 and the second active material layer ATL2. The thickness ratio of the first active material layer ATL1 and the second active material layer ATL2 may be 2:8 to 3:7. The porosity of the first active material layer ATL1 and the second active material layer ATL2 may be 20% to 25%.

[0099] The pore diameter of the first active material layer ATL1 is 0.06 to 0.065 μm, and the porosity of the second active material layer ATL2 may be 0.03 to 0.04 μm. The porosity of the first active material layer may be 100% to 125% of that of the second active material layer.

[0100] The second binder BND2 plays a role in ensuring good adhesion between the first particle PTC1 and the second particle PTC2. Typical examples of the second binder BND2 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. The second binder BND2 may be the same as the first binder BND1 described above, or it may not be the same.

[0101] The second conductive material CDM2 is used to impart conductivity to the electrodes, and any electronically conductive material that does not cause chemical changes in the battery can be used. Examples of the second conductive material CDM2 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 powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof. The second conductive material CDM2 may be the same as the first conductive material CDM1 described above, or it may not be the same.

[0102] The second active material layer ATL2 can be applied 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 current collector COL1 (Figure 6). For example, the current collector COL1 (Figure 6), the first active material layer ATL1, and the second active material layer ATL2 can be arranged in that order.

[0103] The second active material layer ATL2 may have a thickness T2. In one embodiment, T2 may increase as the weight of the first particles PTC1 and the second particles PTC2 contained in the second active material layer ATL2 increases.

[0104] Positive electrode including first and second active material layers Figure 6 is a cross-sectional view of a positive electrode for a lithium secondary battery according to an embodiment of the present invention. Referring to Figure 6, as described above, the positive electrode 10 may include a current collector COL1 and a positive electrode active material layer AML. The positive electrode active material layer AML may be provided on the current collector COL1.

[0105] The positive electrode active material layer AML may contain positive electrode active materials PTC1 and PTC2. The content of the positive electrode active materials PTC1 and PTC2 in the positive electrode active material layer AML may be 90% to 99% by weight relative to 100% by weight of the positive electrode active material layer AML.

[0106] The positive electrode active material layer AML may include binders BND1 and BND2 and conductive materials CDM1 and CDM2. The content of the binders BND1 and BND2 and conductive materials CDM1 and CDM2 may be 0.5% to 5% by weight, respectively, based on 100% by weight of the positive electrode active material layer AML1.

[0107] The positive electrode active material layer AML may include a first active material layer ATL1 and a second active material layer ATL2. By providing a second active material layer ATL2 containing a relatively small amount of nickel-based active material on top of a first active material layer ATL1 containing a large amount of nickel-based active material, the bonding force to the current collector is improved, thereby enabling easier manufacture of the electrode plates and reducing the resistance of the electrode plates. Furthermore, it is possible to provide a lithium secondary battery with superior performance.

[0108] The first active material layer ATL1 may have a thickness T1. In one embodiment, T1 may increase as the weight of the first particles PTC1 and / or second particles PTC2 contained in the first active material layer ATL1 increases. The second active material layer ATL2 may have a thickness T2. In one embodiment, T2 may increase as the weight of the third particles PTC3 contained in the second active material layer ATL2 increases.

[0109] The thickness ratio (T1:T2) of the first active material layer ATL1 and the second active material layer ATL2 can be 2:8 to 3:7. For example, the thickness ratio (T1:T2) of the first active material layer ATL1 and the second active material layer ATL2 can be 5:5. If the thickness ratio (T1:T2) of the first active material layer ATL1 and the second active material layer ATL2 satisfies the numerical range described above, the bonding force of the positive electrode active material layer AML1 to the current collector COL1 is improved, maximizing the battery capacity and energy density while also achieving ease of electrode plate processing.

[0110] As shown in Figures 6 and 7, by introducing the first active material layer ATL1 between the current collector COL1 and the second active material layer ATL2, and mixing the second active material layer PTC2 with the first active material layer PTC1 in an appropriate ratio, the electrode bonding force can be improved and the binder BND content can be reduced. Furthermore, the capacity, density characteristics, high-temperature stability, and lifetime characteristics can be improved. In addition, by including the first active material layer PTC1 in a bimodal form, which is a mixture of single-particle and secondary-particle forms, an even higher density can be achieved.

[0111] Method for manufacturing a positive electrode Figure 14 is a diagram illustrating a method for manufacturing a positive electrode according to one embodiment of the present invention.

[0112] Referring to Figure 14, a method for manufacturing a positive electrode according to one embodiment of the present invention may include providing a current collector COL1, forming a first active material layer ATL1 on the current collector COL1, and forming a second active material layer ATL2 on the first active material layer ATL1. The first active material layer ATL1 may include a layered positive electrode active material as described above in Figure 7. The second active material layer ATL2 may also include an olivine-based positive electrode active material as described above in Figure 7.

[0113] Method for manufacturing the first active material layer A method for producing the first positive electrode active material layer according to embodiments of the present invention will be described in detail. A high-nickel precursor can be prepared. The high-nickel precursor may contain Ni of chemical formula 1 as described above. The content of Ni relative to the total metal content in the high-nickel precursor can be greater than 80 at%. In one embodiment, the high-nickel precursor may further contain Co and Mn.

[0114] In one embodiment, a high-nickel precursor can be obtained by coprecipitation. For example, the coprecipitation method may include dissolving a transition metal raw material in a solvent such as distilled water, and continuously introducing the transition metal salt solution into a reactor together with a chelating agent and a basic aqueous solution to induce precipitation. After recovering the precipitate in slurry form, the slurry solution is filtered and dried to obtain a high-nickel precursor, which is a metal composite oxide.

[0115] In the present invention, the transition metal raw material may include a metal salt of Ni. The transition metal raw material may further include at least one metal salt from Co and Mn. The metal salt can be a sulfate, nitrate, acetate, halide, hydroxide, etc., and is not particularly limited as long as it is soluble in the solvent. The transition metal raw material according to this embodiment may include nickel salts, cobalt salts, and manganese salts. The transition metal raw materials can be mixed by adjusting the molar ratio so that the high-nickel precursor has a Ni content of 80 at% or more.

[0116] A mixture can be formed by mixing a high-nickel precursor and a lithium source in a fixed ratio. For example, the high-nickel precursor and lithium source can be mixed in a molar ratio of about 1:1. The lithium source may include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0117] The mixture can be dried by removing the solvent. The dried mixture can then be calcined. The calcination temperature may be 700°C to 1,000°C or 900°C to 1,000°C. The calcination can be carried out in an oxidizing atmosphere such as air or oxygen. The heat treatment time for the calcination can be 10 to 30 hours. In another embodiment of the present invention, an additional pre-calcination may be performed at 150°C to 800°C before the calcination process.

[0118] In one embodiment of the present invention, the firing process can be carried out after adding a molten metal to the mixture. The molten metal may be a compound containing at least one metal selected from the group consisting of Zr, La, S, and Nb. By using the molten metal, the layered cathode active material contained in the first cathode active material layer can be smoothly formed into a single-particle form. In addition, the average particle size of the layered cathode active material can be increased.

[0119] A layered cathode active material can be formed from a mixture containing a high-nickel precursor and a lithium source through the aforementioned calcination process. The synthesized layered cathode active material can then be subjected to a grinding process.

[0120] A coating process can be performed on the pulverized layered cathode active material. Specifically, the layered cathode active material and the coating raw material can be added to a solvent and mixed. For example, the coating raw material may include boron and / or aluminum. After filtering and drying the layered cathode active material, a surface treatment can be performed on the layered cathode active material. The surface treatment may include a heat treatment process in an oxidizing atmosphere such as air or oxygen. The surface treatment can be performed at a temperature of 500°C to 800°C.

[0121] In another embodiment of the present invention, the coating step may include a dry coating step. For example, the layered cathode active material and the coating raw material can be placed in a dry coating machine without a solvent and stirred to mix them. The surface treatment can then be performed on the resulting dry mixture.

[0122] Second active material layer manufacturing method A method for producing the second active material layer according to embodiments of the present invention will be described in detail. The iron phosphate precursor, lithium source, carbon source, and dopant source can be added to a solvent and mixed. For example, the solvent may be water, ethanol, etc. The iron phosphate precursor may be a compound containing both iron (Fe) and phosphorus (P), or a mixture of an iron (Fe)-containing compound and a phosphorus (P)-containing compound. For example, the iron phosphate precursor may include FePO4·H2O, or a mixture of FeSO4 and H3PO4.

[0123] The lithium source may include at least one selected from the group consisting of lithium oxide, lithium hydroxide, lithium chloride, lithium nitrate, lithium nitrite, lithium formate, lithium acetate, lithium oxalate, lithium carbonate, lithium phosphate, lithium hydrogen phosphate, lithium dihydrogen phosphate, and lithium citrate.

[0124] The carbon source may include at least one selected from the group consisting of glucose, sucrose, fructose, cellulose, starch, citric acid, polyacrylic acid, polyethylene glycol, and dopamine.

[0125] The dopant source may include oxides containing a dopant metal and / or chlorides containing a dopant metal. For example, the dopant source may include at least one selected from the group consisting of titanium oxide, magnesium oxide, vanadium oxide, and niobium oxide.

[0126] The mixture can be subjected to wet grinding. This wet grinding can be carried out using a conventional wet mill with temperature control. Specifically, the wet grinding can utilize at least one selected from a bead mill, ball mill, attrition mill, apex mill, super mill, and basket mill. Through the wet grinding process, the particles in the mixture can be ground to a fine size.

[0127] The solvent can be removed from the mixture to form a dried mixture. In one embodiment of the present invention, forming a dried mixture may involve a direct evaporation method of the mixture. For example, the direct evaporation method may include static drying or spray drying.

[0128] The dried mixture can be calcined under an inert atmosphere. The inert atmosphere may be a nitrogen atmosphere and / or an argon atmosphere. The calcination temperature may be 500°C to 1000°C or 600°C to 800°C. The calcination time may be 4 to 20 hours or 6 to 12 hours. By calcining the dried mixture, an olivine-based cathode active material containing the compound of chemical formula 2 described above can be formed. A dry grinding process can be performed on the calcined olivine-based cathode active material.

[0129] 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 or 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, the invention is not limited thereto.

[0130] The wet process may involve mixing a positive electrode active material, a conductive material, and a binder in a solvent to produce a positive electrode mixture, and then coating the mixture onto a current collector for drying and rolling. 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.

[0131] The dry process may involve dry mixing a positive electrode active material, a dry conductive material, and a dry binder without a solvent to produce a positive electrode mixture, and then placing the mixture on a current collector and rolling it.

[0132] Subsequently, a roll pressing process, a slitting process, and a notching process can be sequentially performed on the positive electrode 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.

[0133] Examples and comparative examples of the present invention are described below. However, the examples described below are merely embodiments of the present invention, and the present invention is not limited to the examples described below.

[0134] Manufacturing Example 1 (1st particle production) High-nickel precursors were produced using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as raw materials for nickel-based metal hydroxides in a molar ratio of 92:5:2 to prepare a mixture of metal raw materials. The mixture of metal raw materials, aqueous ammonia, and sodium hydroxide were added to a reactor and reacted. The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 210°C for 24 hours to obtain a small-grain precursor (Ni) with an average particle size of approximately 4 μm. 0.920 Co 0.05 Mn 0.02 We obtained OH2 powder.

[0135] A high-nickel precursor and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. Lithium and a transition metal were mixed in a molar ratio of approximately 1:1. The transition metal was the sum of the transition metals (Ni + Co + Mn) contained in the high-nickel precursor. A flux was added to the mixture, and the high-nickel cathode active material was synthesized by heat treatment (i.e., calcination process) at approximately 750°C for 15 hours in an oxygen atmosphere. The high-nickel cathode active material was pulverized in a jet mill at a pressure of 3 bar.

[0136] The first cathode active material, which is a high-nickel cathode active material, was washed by adding it to distilled water. Boron oxide and aluminum oxide, corresponding to 3 mol% of the total transition metals in the high-nickel cathode active material, were added to perform boron and aluminum coating. The first cathode active material was dried at 150°C for 12 hours, and then heat-treated (i.e., surface-treated) at approximately 700°C in an oxygen atmosphere for 15 hours to produce the first particles.

[0137] (2nd particle) A molar ratio of 1:1.03 was used to mix iron phosphate precursor Fe1PO4·H2O with lithium carbonate, 2500 ppm titanium dioxide, and 8 wt% glucose in water. The mixture was then wet-milled using a ball mill. After evaporating the mixture in a heated oven tray, it was dried in a vacuum oven at 85°C for 4 hours. The dried mixture was calcined at 650°C for 10 hours under a nitrogen atmosphere. The calcined material was then pulverized to obtain second particles in single-particle form.

[0138] Example 1: Manufacturing of a positive electrode containing a first active material layer and a second active material layer A first active material slurry was prepared by dispersing the first particles prepared through Production Example 1, the second particles prepared through Production Example 2, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) in N-methylpyrrolidone in a weight ratio of 0.85:0.05:0.08:0.02.

[0139] The second active material slurry was prepared by dispersing the second particles, second binder (polyvinylidene fluoride), and second conductive material (carbon black) prepared through manufacturing example 2 in N-methylpyrrolidone in a weight ratio of 0.9:0.08:0.02.

[0140] The first active material slurry was applied to and dried on a 12 μm thick aluminum (Al) thin film, which was a positive electrode current collector, to form a first active material layer. The second active material slurry was applied to and dried on the first active material layer to form a second active material layer. At this time, the first and second active material layers were formed such that the weight ratio of the first active material slurry to the first particles in the second active material slurry was 30 wt%. 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 stacked.

[0141] Example 2: Manufacturing of a positive electrode containing a first active material layer and a second active material layer The positive electrode was manufactured in the same manner as in Example 1, except that the weight ratio of the first and second particles in the first active material slurry was set to 0.80:0.20.

[0142] Example 3: Manufacturing of a positive electrode containing a first active material layer and a second active material layer The positive electrode was manufactured in the same manner as in Example 1, except that the weight ratio of the first and second particles in the first active material slurry was set to 0.90:0.10.

[0143] Comparative Example 1: Production of a positive electrode containing one active material layer that does not contain the first particle. The second particles, first binder (polyvinylidene fluoride), and first conductive material (carbon black) prepared through Manufacturing Example 2 were dispersed in N-methylpyrrolidone in a weight ratio of 0.9:0.08:0.02 to produce a first active material slurry. The first active material slurry was applied to and dried on a 12 μm thick aluminum (Al) thin film, which was a positive electrode current collector, to form a first active material layer. A positive electrode was manufactured by performing a roll press, in which the aluminum current collector and the first active material layer were sequentially laminated.

[0144] Comparative Example 2: Manufacturing of a positive electrode containing one active material layer containing the first and second particles. A first active material slurry was prepared by dispersing the first particles prepared through Production Example 1, the second particles prepared through Production Example 2, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone in a weight ratio of 0.7:0.2:0.08:0.02. The first active material slurry was applied to and dried on a 12 μm thick aluminum (Al) thin film, which was a positive electrode current collector, to form a first active material layer. A positive electrode was manufactured by performing a roll press, in which the aluminum current collector and the first active material layer were sequentially laminated.

[0145] Comparative Example 3: Production of a cathode containing a first active material layer in which the first particles make up less than 70% A first active material slurry was prepared by dispersing the first particles prepared through Production Example 1, the second particles prepared through Production Example 2, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) in N-methylpyrrolidone in a weight ratio of 0.6:0.3:0.08:0.02.

[0146] The second active material slurry was prepared by dispersing the second particles, second binder (polyvinylidene fluoride), and second conductive material (carbon black) prepared through manufacturing example 2 in N-methylpyrrolidone in a weight ratio of 0.9:0.08:0.02.

[0147] The first active material slurry was applied to and dried on a 12 μm thick aluminum (Al) thin film, which was a positive electrode current collector, to form a first active material layer. The second active material slurry was applied to and dried on the first active material layer to form a second active material layer. 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.

[0148] Comparative Example 4: Production of a cathode containing a first active material layer in which the first particles make up more than 90%. A first active material slurry was prepared by dispersing the first particles prepared through Production Example 1, the second particles prepared through Production Example 2, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) in N-methylpyrrolidone in a weight ratio of 0.85:0.05:0.08:0.02.

[0149] The second active material slurry was prepared by dispersing the second particles, second binder (polyvinylidene fluoride), and second conductive material (carbon black) prepared through manufacturing example 2 in N-methylpyrrolidone in a weight ratio of 0.9:0.08:0.02.

[0150] The first active material slurry was applied to and dried on a 12 μm thick aluminum (Al) thin film, which was a positive electrode current collector, to form a first active material layer. The second active material slurry was applied to and dried on the first active material layer to form a second active material layer. 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.

[0151] Manufacturing of lithium-ion batteries A 2032 type coin half-cell was fabricated using a prepared positive electrode and a lithium metal counter electrode as the relative electrode. A separator (thickness: approximately 16 μm) made of porous polyethylene (PE) film was interposed between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected to fabricate a lithium secondary battery. As the electrolyte, an electrolyte solution obtained by mixing 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3 was used.

[0152] Evaluation Example 1: Adhesion Strength Evaluation The peel strength of the positive electrode plates manufactured in Example 1, Example 2, and Comparative Examples 1 to 4 was measured according to the ASTM D3330 standard. The instruments used for measurement were a UTM and an Instron 3345.

[0153] Positive electrode plates with active material layers on both sides, manufactured in Examples 1, 2, and Comparative Examples 1 to 4, were cut to a size of 25 mm x 150 mm to prepare 20 test pieces each. At room temperature, adhesive was coated onto a glass substrate, the positive electrode plate was attached to the adhesive, roll-pressed, and then one end of the positive electrode plate was folded 180°. The force applied was measured while pulling at a speed of 100 mm / min in the opposite direction of the other end. The evaluation results are shown in Table 1 below. The crack occurrence rate is the percentage of test pieces in which a crack (break) occurred in the positive electrode active material layer on one side of the positive electrode plate that did not come into contact with the adhesive during the 180° folding process. The peel strength is the average value of the 20 test pieces. A higher peel strength indicates higher adhesive strength.

[0154] The adhesive strength of one side of the positive electrode current collector was measured as the A-side adhesive strength, and the adhesive strength of the other side of the positive electrode current collector was measured as the B-side adhesive strength.

[0155] [Table 1]

[0156] As shown in Table 1, the peel strength increased in the positive electrodes of Examples 1 to 3 compared to the positive electrodes of Comparative Examples 1 to 3. A graph of the above table is shown in Figure 12.

[0157] Therefore, it was confirmed that Examples 1 and 3 have significantly improved adhesive force between the positive electrode active material layer and the current collector, and / or cohesive force of the positive electrode active material layer, compared to the positive electrodes of Comparative Examples 1 to 3.

[0158] Evaluation Example 2: Interfacial Resistance Evaluation The interfacial resistance evaluation for the positive electrode active material of Example 1, Example 2, and Comparative Examples 1 to 4 was measured, and the results are shown in Table 2 below.

[0159] The interfacial resistance of lithium batteries from Example 1, Example 2, and Comparative Examples 1 to 4 was measured at 25°C using an electrode resistance measurement system (Hioki, RM2610).

[0160] Using an electrode resistance measurement system (Hioki, RM2610), the probe was positioned on the positive electrode so that the positive electrode active material layer faced the probe. A constant current was passed through the surface of the positive electrode active material layer, and the volume resistivity of the positive electrode active material layer and the interfacial resistance between the positive electrode active material layer and the positive electrode current collector were measured from the surface potential distribution.

[0161] [Table 2]

[0162] As shown in Table 2, the interfacial resistances of Examples 1 to 3 are smaller than those of Comparative Example 1 to Comparative Example 3. It was determined that Examples 1 to 3 of the present invention, in which Ni is blended into the lower layer plate at a concentration of 70% or more, have low interfacial resistances.

[0163] Evaluation Example 3: Pallet Resistance Evaluation For each of the positive electrodes in Example 1, Example 2, and Comparative Examples 1 to 4, the pallet resistance was measured at 25°C using an electrode resistance measurement system (Hioki, RM2610), and the measurement results are shown in Table 3 below.

[0164] Using an electrode resistance measurement system (Hioki, RM2610), a probe was placed on the positive electrode so that the positive electrode active material layer faced the probe. A constant current was passed through the surface of the positive electrode active material layer, and the volume resistivity of the positive electrode active material layer and the interfacial resistance between the positive electrode active material layer and the positive electrode current collector were measured from the surface potential distribution. The volume resistivity of the positive electrode active material layer was considered as the pallet resistivity of the positive electrode active material layer.

[0165] [Table 3]

[0166] As shown in Table 3, the pallet resistivity of Examples 1 to 3 was reduced compared to the pallet resistivity of Comparative Examples 1 to 4. Figure 13 shows graphs of the interface resistance and pallet resistivity. [Explanation of Symbols]

[0167] 10 positive electrode AML positive electrode active material layer ATL1 1st active material layer ATL2 2nd active material layer COL1 current collector BND1 First Binder BND2 Second Binder CDM1 First conductive material CDM2 Second conductive material COL1 current collector COL2 current collector PTC1, PTC2 Positive electrode active material particles

Claims

1. Current collector and, The first active material layer on the current collector, The second active material layer on the first active material layer, Includes, The first active material layer comprises a first particle containing a layered cathode active material, a second particle containing an olivine-based cathode active material, a first conductive material, and a first binder. The second active material layer comprises the second particles, the second conductive material, and the second binder. A positive electrode for a lithium secondary battery, wherein the content of the first particles in the first active material layer is 70% or more and 90% or less.

2. The second active material layer contains the first particle, The positive electrode for a lithium secondary battery according to claim 1, wherein the content of the first particles in the second active material layer is greater than 0 and less than or equal to 30%.

3. The positive electrode for a lithium secondary battery according to claim 1, wherein the first particle and the second particle have a single-particle shape.

4. The first particle has a secondary particle shape formed by the aggregation of a plurality of primary particles. The positive electrode for a lithium secondary battery according to claim 1, wherein the average size of the first primary particles is 100 nm to 200 nm.

5. The average particle size (D) of the first particle 50 The positive electrode for a lithium secondary battery according to claim 4, wherein the thickness of the electrode is 10 μm to 14 μm.

6. With respect to the total weight of the first and second active material layers, The positive electrode for a lithium secondary battery according to claim 1, wherein the weight of the first particle is 25% to 35% of the total weight.

7. The positive electrode for a lithium secondary battery according to claim 1, wherein the second particle comprises a compound represented by the following chemical formula 2. [Chemical 2] Li a2 Fe x2 B y2 PO 4-b2 In the aforementioned chemical formula 2, 0.8 ≤ a² ≤ 1.2, 0.1 ≤ x² ≤ 1.0, 0.001 ≤ y² ≤ 0.05, and 0 ≤ b² ≤ 0.

05. In the aforementioned chemical formula 2, x² + y² ≤ 1, In the above chemical formula 2, B is Ti, Mg, V, or Nb.

8. The positive electrode for a lithium secondary battery according to claim 1, wherein the first particle comprises a compound represented by the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Co y1 Mn z1 X c1 O 2-b1 In the aforementioned chemical formula 1, 0.8 ≤ a1 ≤ 1.2, 0.8 ≤ x1 ≤ 1.0, 0 ≤ y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0 ≤ c1 ≤ 0.05, and 0 ≤ b1 ≤ 0.

05. In the aforementioned chemical formula 1, x1 + y1 + z1 + c1 ≤ 1, In the above chemical formula 1, X is Al, Ti, Mg, Zr, Mo, or Nb.

9. The second active material layer does not contain the first particle. The positive electrode for a lithium secondary battery according to claim 1.

10. The positive electrode for a lithium secondary battery according to claim 1, wherein the porosity of the first active material layer is 100% to 125% of that of the second active material layer.

11. Current collector and, The first active material layer on the current collector, The second active material layer on the first active material layer, Includes, The first active material layer comprises first particles, second particles, first conductive material, and first binder. The second active material layer comprises the second particles, the second conductive material, and the second binder. The first particle comprises a layered cathode active material, The aforementioned second particle contains an olivine-based cathode active material, With respect to the total weight of the first and second active material layers, A positive electrode for a lithium secondary battery, wherein the weight of the first particle is 25% to 35% of the total weight.

12. The second active material layer contains the first particle, The positive electrode for a lithium secondary battery according to claim 11, wherein the content of the first particles in the first active material layer is at least twice the content of the first particles in the second active material layer.

13. The positive electrode for a lithium secondary battery according to claim 11, wherein the content of the first particles in the first active material layer is 70% or more and 90% or less.

14. The positive electrode for a lithium secondary battery according to claim 11, wherein the second particle comprises a compound represented by the following chemical formula 2. [Chemical 2] Li a2 Fe x2 B y2 PO 4-b2 In the aforementioned chemical formula 2, 0.8 ≤ a² ≤ 1.2, 0.1 ≤ x² ≤ 1.0, 0.001 ≤ y² ≤ 0.05, and 0 ≤ b² ≤ 0.

05. In the aforementioned chemical formula 2, x² + y² ≤ 1, In the above chemical formula 2, B is Ti, Mg, V, or Nb.

15. The positive electrode for a lithium secondary battery according to claim 11, wherein the first particle comprises a compound represented by the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Co y1 Mn z1 X c1 O 2-b1 In the aforementioned chemical formula 1, 0.8 ≤ a1 ≤ 1.2, 0.8 ≤ x1 ≤ 1.0, 0 ≤ y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0 ≤ c1 ≤ 0.05, and 0 ≤ b1 ≤ 0.

05. In the aforementioned chemical formula 1, x1 + y1 + z1 + c1 ≤ 1, In the above chemical formula 1, X is Al, Ti, Mg, Zr, Mo, or Nb.

16. The positive electrode for a lithium secondary battery according to claim 11, wherein the content of the first particles in the second active material layer is 30% or less.

17. The first particle has a secondary particle shape formed by the aggregation of a plurality of primary particles. The second particle comprises at least one selected from the group consisting of lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP), The positive electrode for a lithium secondary battery according to claim 11, wherein the first particle comprises a compound represented by the following chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Co y1 Mn z1 X c1 O 2-b1 In the aforementioned chemical formula 1, 0.8 ≤ a1 ≤ 1.2, 0.8 ≤ x1 ≤ 1.0, 0 ≤ y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0 ≤ c1 ≤ 0.05, and 0 ≤ b1 ≤ 0.

05. In the aforementioned chemical formula 1, x1 + y1 + z1 + c1 ≤ 1, In the above chemical formula 1, X is Al, Ti, Mg, Zr, Mo, or Nb.

18. The first particle has a secondary particle shape formed by the aggregation of a plurality of primary particles. The positive electrode for a lithium secondary battery according to claim 11, wherein the second particle has a primary particle shape that is a single particle.

19. The diameter of the pores in the first active material layer is 0.06 to 0.065 μm. The positive electrode for a lithium secondary battery according to claim 11, wherein the porosity of the second active material layer is 0.03 to 0.04 μm.

20. A lithium secondary battery comprising the positive electrode described in claim 1.

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