Positive electrode and lithium secondary battery including the same

Abstract

To provide a positive electrode for a lithium secondary battery, by which the binding strength of a positive electrode active material layer for a current collector is increased, the resistance of an electrode plate is reduced, and the electrode plate can be manufactured easily.SOLUTION: The present invention relates to a positive electrode and a lithium secondary battery including the same. More specifically, the positive electrode includes a current collector, a first active material layer including first particles, a first binder, and a first conductive material and existing on the current collector, and a second active material layer including second particles, a second binder, and a second conductive material and existing on the first active material layer. The first particles contain a compound with a layered structure. The second particles contain a compound with an olivine structure. The second particles are single particles. The first binder and the first conductive material form a first functional additive. The second binder and the second conductive material form a second functional additive. The weight ratio of the first functional additive in the first active material layer is less than the weight ratio of the second functional additive in the second active material layer.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a positive electrode and a lithium secondary battery including the same, and more particularly to a positive electrode including an olivine-based lithium compound and a lithium secondary battery including the same. [Background technology]

[0002] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density and high-capacity secondary batteries has been increasing rapidly. Accordingly, research and development to improve the performance of lithium secondary batteries has been actively conducted.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, which contain active materials that allow the intercalation and deintercalation of lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted / deintercalated at the cathode and anode. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a positive electrode for a lithium secondary battery that can easily manufacture an electrode plate by increasing the adhesive strength of a positive electrode active material layer to a current collector and reducing the resistance of the electrode plate, and also provides a lithium secondary battery that has excellent capacity and life characteristics, as well as high operating voltage and energy density. [Means for solving the problem]

[0005] A positive electrode for a lithium secondary battery according to one embodiment of the present invention may include a first active material layer on the current collector, the first particles, a first binder, and a first conductive material, and a second active material layer on the first active material layer, the first particles comprising a layered structure compound represented by Chemical Formula 1 below, the second particles comprising an olivine structure compound represented by Chemical Formula 2 below, the second particles being single particles, the first binder and the first conductive material comprising a first functional additive, and the second binder and the second conductive material comprising a second functional additive, and a weight ratio of the first functional additive in the first active material layer may be smaller than a weight ratio of the second functional additive in the second active material layer. [Chemical formula 1] Li a1 Ni x1 Co y1 Mn z1 B1 c1 O 2-b1

[0006] In the formula 1, 0.8≦a1≦1.2, 0.5≦x1≦0.8, 0≦y1≦0.3, 0.1≦z1≦0.5, 0≦c1≦0.1, 0≦b1≦0.05, and x1+y1+z1+c1=1; and B1 includes at least one selected from the group consisting of Ti, Mg, V, Nb, and Al; [Chemical formula 2] Li a2 Mn x2 Fe y2 B2 z2 PO 4-b2

[0007] In Chemical Formula 2, 0.8≦a2≦1.2, 0.4≦x2≦0.8, 0≦y2≦0.6, 0≦z2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1, and B2 may include at least one selected from the group consisting of Al, Ti, V, and Mg.

[0008] A lithium secondary battery according to an embodiment of the present invention may include the above-described positive electrode. [Effects of the Invention]

[0009] The positive electrode for a lithium secondary battery according to an embodiment of the present invention includes a large amount of a nano-sized olivine-based compound, and has improved binding strength to a current collector, thereby facilitating the manufacture of an electrode plate and reducing the resistance of the electrode plate.

[0010] The lithium secondary battery according to an embodiment of the present invention may have excellent capacity and life characteristics, as well as high operating voltage and energy density. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a conceptual diagram illustrating a lithium secondary battery according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view showing a lithium secondary battery according to an embodiment. [Figure 3] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the lithium secondary battery having a cylindrical battery shape. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, the battery having a prismatic shape. [Figure 5] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment, in the form of a pouch-shaped battery. [Figure 6] 1 is a cross-sectional view of a positive electrode for a secondary battery according to an embodiment of the present invention. [Figure 7] FIG. 2 is an enlarged view of a first active material layer according to an embodiment of the present invention. [Figure 8] FIG. 2 is an enlarged view of a first active material layer according to an embodiment of the present invention. [Figure 9] FIG. 2 is an enlarged view of a first active material layer according to an embodiment of the present invention. [Figure 10] FIG. 3 is an enlarged view of a second active material layer according to one embodiment of the present invention. [Figure 11] FIG. 4 is an enlarged view of a positive electrode active material layer according to a comparative example of the present invention. [Figure 12] 1 is a SEM image of a first particle according to an embodiment of the present invention. [Figure 13]10 is an SEM image of second particles according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] In this specification, when a component is referred to as being on another component, it means that the component may be formed directly on the other component, or that a third component may be interposed between them. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms and may undergo various modifications. The description of the present embodiments is provided solely to ensure complete disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0013] In this specification, when a component is referred to 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. Also, in the drawings, the thickness of the components is exaggerated for the sake of efficient explanation of the technical content. Parts designated with the same reference numerals throughout the specification refer to the same components.

[0014] Unless otherwise specified herein, the singular can also include the plural. Furthermore, unless otherwise specified, "A or B" can mean "including A, including B, or including A and B." As used herein, "comprises" and / or "comprising" does not exclude the presence or addition of one or more other elements to the referenced element.

[0015] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0016] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope (TEM) or scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and data analysis can be performed to count the number of particles in each particle size range, after which the average particle size (D50) can be calculated. Alternatively, the average particle size (D50) can be measured using a laser diffraction method. More specifically, when measuring by the laser diffraction method, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT3000), and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. The average particle size (D50) based on 50% of the particle size distribution in the measuring device can then be calculated.

[0017] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment 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.

[0018] The positive electrode 10 and the negative electrode 20 may be separated from each other by a separator 30. The separator 30 may be disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be in contact with an electrolyte solution ELL. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated in the electrolyte solution ELL.

[0019] The electrolyte ELL can be a medium for transferring lithium ions between the positive electrode 10 and the negative electrode 20. In the electrolyte ELL, the lithium ions can pass through the separator 30 and move toward the positive electrode 10 or the negative electrode 20.

[0020] 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. A detailed description of the positive electrode active material layer AML1 according to an embodiment of the present invention will be provided below with reference to FIGS. 6 to 10. The current collector COL1 may be made of aluminum, but is not limited thereto.

[0021] negative electrode 20 The negative electrode 20 for a 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.

[0022] For example, the negative electrode active material layer AML2 may contain 90 to 99 wt % of the negative electrode active material, 0.5 to 5 wt % of the binder, and 0 to 5 wt % of the conductive material.

[0023] The binder serves to firmly adhere the negative electrode active material particles to each other and to firmly adhere the negative electrode active material to the current collector COL 2. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0024] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0025] The water-based 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.

[0026] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulose-based compound that can impart viscosity. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0027] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0028] The conductive material is used to impart conductivity to the electrode, and any material that is electronically conductive without causing a chemical change in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0029] As the current collector COL2, a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, or a combination thereof can be selected and used.

[0030] negative electrode active material The negative electrode active material in the negative electrode active material layer AML2 includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping with lithium, or a transition metal oxide.

[0031] The material capable of reversibly inserting / desorbing lithium ions can be a carbon-based negative electrode active material, for example, it can include crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, etc.

[0032] As the alloy of lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0033] As the material capable of doping and undoping with 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 (Q is selected from an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element (excluding Si), a group 15 element, a group 16 element, a transition metal, a rare earth element, and a combination thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn-based alloy, or a combination thereof.

[0034] 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 the surfaces of the silicon particles coated with amorphous carbon. For example, it may include secondary particles (cores) formed by assembling primary silicon particles and a first coating layer (shell) of amorphous carbon located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, coating the primary silicon particles with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0035] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and a first coating layer of amorphous carbon disposed on the core.

[0036] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material.

[0037] 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. As such separator 30, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and it goes without saying that 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 may also be used.

[0038] Separator 30 can include a porous substrate and a first coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0039] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0040] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0041] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0042] The organic material and the inorganic material may be mixed in one first coating layer, or may be stacked in a form in which a first coating layer containing an organic material and a first coating layer containing an inorganic material are stacked.

[0043] Electrolyte ELL The electrolyte ELL for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0044] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.

[0045] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0046] Examples of carbonate 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).

[0047] Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0048] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0049] The non-aqueous organic solvents can be used alone or in combination of two or more.

[0050] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed together, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0051] Lithium salts are dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. 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 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethene sulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium bis(oxalato)borate (LiBOB).

[0052] Lithium secondary battery Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 2 to 5 are schematic diagrams showing lithium secondary batteries according to embodiments, with FIG. 2 illustrating a cylindrical type, FIG. 3 illustrating a prismatic type, and FIGS. 4 and 5 illustrating pouch types. Referring to FIGS. 2 to 4, a 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 shown in FIG. 2. Also, in FIG. 3, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 4 and 5, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting current generated in the electrode assembly 40 to the outside.

[0053] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0054] 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 FIG. 6, as described above, the positive electrode 10 may include a current collector COL1 and a positive electrode active material layer AML1. The positive electrode active material layer AML1 may be provided on the current collector COL1.

[0055] The positive electrode active material layer AML1 may include positive electrode active materials PTC1 and PTC2, as described below. The content of the positive electrode active materials PTC1 and PTC2 in the positive electrode active material layer AML1 may be 90 wt % to 99 wt % relative to 100 wt % of the positive electrode active material layer AML1.

[0056] The positive electrode active material layer AML1 may include binders BND1 and BND2 and conductive materials CDM1 and CDM2, as described below. The contents of the binders BND1 and BND2 and the conductive materials CDM1 and CDM2 may be 2.4 wt % to 6 wt % respectively, based on 100 wt % of the positive electrode active material layer AML1.

[0057] The positive electrode active material layer AML1 may include a first active material layer ATL1 and a second active material layer ATL2. By providing the second active material layer ATL2 on the first active material layer ATL1, the positive electrode active material layer AML1 contains a large amount of nano-sized olivine-based compounds, and improves the binding strength to the current collector, thereby facilitating the manufacture of an electrode plate and reducing the resistance of the electrode plate. This also allows for the provision of a lithium secondary battery with excellent performance.

[0058] 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 included 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 second particles PTC2 included in the second active material layer ATL2 increases.

[0059] The thickness T1 of the first active material layer ATL1 may be smaller than the thickness T2 of the second active material layer ATL2. For example, the thickness ratio (T1:T2) of the first active material layer ATL1 to the second active material layer ATL2 may be 1:99 to 49:51. When the thickness ratio (T1:T2) of the first active material layer ATL1 to the second active material layer ATL2 satisfies the above-described numerical range, the bonding strength of the positive electrode active material layer AML1 to the current collector COL1 is improved, making it easier to manufacture the electrode plate and reducing the electrode plate resistance. In addition, a lithium secondary battery with excellent performance can be provided.

[0060] 7 to 9 are enlarged views of a first active material layer ATL1 according to an embodiment of the present invention, and Fig. 10 is an enlarged view of a second active material layer ATL2 according to an embodiment of the present invention.

[0061] 7 to 9, the first active material layer ATL1 may include first particles PTC1 and a first functional additive FAD1. The first functional additive FAD1 may include a first binder BND1 and a first conductive material CDM1.

[0062] The positive electrode active material layer AML1 includes the first active material layer ATL1 containing the first particles PTC1, thereby reducing the content of the first functional additive FAD1. For example, the weight ratio of the first functional additive FAD1 in the first active material layer ATL1 may be 0.024 to 0.04. The "weight ratio of the first functional additive FAD1 in the first active material layer ATL1" may be defined as the weight of the first functional additive FAD1 relative to the weight of the first active material layer.

[0063] For example, 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, and 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.

[0064] 10, the second active material layer ATL2 may include second particles PTC2 and a second functional additive FAD2. The second functional additive FAD2 may include a second binder BND2 and a second conductive material CDM2.

[0065] In the present invention, the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be greater than the weight ratio of the first functional additive FAD1 in the first active material layer ATL1.

[0066] The weight ratio of the second functional additive FAD2 to the weight ratio of the first functional additive FAD1 (weight ratio of second functional additive / weight ratio of first functional additive) may be 1.5 to 3. When the weight ratio of the second functional additive FAD2 to the weight ratio of the first functional additive FAD1 satisfies the above-described numerical range, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 is improved, making it easier to manufacture an electrode plate and reducing the resistance of the electrode plate. In addition, a lithium secondary battery with excellent performance can be provided.

[0067] For example, the weight ratio of the second functional additive FAD2 in the second active material layer ATL2 may be 0.04 to 0.06. The "weight ratio of the second functional additive FAD2 in the second active material layer ATL2" may be defined as the weight of the second functional additive FAD2 relative to the weight of the second active material layer.

[0068] The content of the second binder BND2 may be greater than the content of the first binder BND1, for example, 2.0 to 3.0 parts by weight per 100 parts by weight of the second active material layer ATL2.

[0069] The content of the second conductive material CDM2 may be greater than the content of the first conductive material CDM1, and may be 2.0 to 3.0 parts by weight per 100 parts by weight of the second active material layer ATL2.

[0070] The binders BND1 and BND2 serve to firmly adhere the positive electrode active material particles PTC1 and PTC2 to each other and to firmly adhere the positive electrode active material PTC1 to the current collector COL1. Representative examples of binders BND1 and BND2 include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, 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.

[0071] The conductive materials CDM1 and CDM2 are used to impart conductivity to the electrodes, and any material that is electronically conductive and does not cause chemical changes in the battery that is constructed can be used. Examples of conductive materials CDM1 and CDM2 include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0072] The interface between the first active material layer ATL1 and the second active material layer ATL2 may not be clearly distinguishable in an SEM image, etc. However, the interface between the first active material layer ATL1 and the second active material layer ATL2 can be inferred from differences in constituent materials, composition, etc. between the layers.

[0073] Hereinafter, the first particles PTC1 and the second particles PTC2 will be described in more detail.

[0074] 1st particle PTC1 Referring again to FIG. 7, the first particle PTC1 may have a single particle shape. In this specification, a single particle may refer to a single particle without an internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles are morphologically present in an independent phase without aggregation. For example, a single particle may be a single crystal. Alternatively, a single particle may be a particle containing several crystals. A single particle may be in a singly separated form. Alternatively, a single particle may be in a form in which 2 to 100 single particles are attached to each other.

[0075] In one embodiment, the first particle PTC1 may have a shape composed of one single particle. In another embodiment, the first particle PTC1 may have a shape in which a plurality of single particles are attached to one another. The cathode active material according to the present invention includes the first particle PTC1 in the form of a single particle, thereby providing a high capacity and high energy density of a secondary battery. In this specification, the first particle PTC1, which is a single particle, may be defined as a small particle SP.

[0076] In one embodiment, the first particle PTC1 may include a first coating layer on its surface. By including the first coating layer, the first particle PTC1 can effectively prevent structural collapse due to repeated charge and discharge, thereby improving the lifespan of the secondary battery.

[0077] The first coating layer may include a boron-containing compound, an aluminum-containing compound, or a combination thereof. The metal-containing compound in the first coating layer may be, for example, a metal oxide, a metal hydroxide, a metal carbonate, a composite thereof, or a mixture thereof. The metal-containing compound may further include other metals or non-metal elements. For example, the first coating layer may further include lithium, manganese, and / or nickel, etc.

[0078] A method for measuring the metal content in the first coating layer of the first particles PTC1 may include performing scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) on the first particles PTC2. The boron and / or aluminum content in the first coating layer may be determined through the analysis. In addition to SEM-EDS, methods for measuring the metal content in the first coating layer may also include inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0079] The size of the first particles PTC1 may be in the micron range. By incorporating the first active material layer ATL1 containing the first particles PTC1, the positive electrode active material layer AML1 can have a high binding strength to the current collector while containing a large amount of nano-sized olivine-based compounds. This allows for easy manufacture of the electrode plate, and reduces the resistance of the electrode plate. Furthermore, a lithium secondary battery with excellent performance can be provided.

[0080] The average particle size of the first particles PTC1 may be 2 μm to 15 μm, 3 μm to 10 μm, or 2 μm to 5 μm.

[0081] In one embodiment, approximately 30 first particles PTC1 are randomly selected from an electron microscope photograph of the positive electrode active material, and their particle sizes are measured. The diameter of the particles whose cumulative volume is 50% by volume in the particle size distribution can be obtained as the average particle size (D50).

[0082] The first particles PTC1 may include a lithium-nickel-based composite oxide as a nickel-based active material. As one example, the first particles PTC1 may include a high-nickel-based positive electrode active material containing a high content of nickel. The high-nickel-based positive electrode active material can provide high capacity and high performance. As another example, the first particles PTC1 may include a mid-nickel-based positive electrode active material containing a medium content of nickel. The mid-nickel-based positive electrode active material can provide high capacity and high performance.

[0083] The first particles PTC1 may include a lithium nickel-based composite oxide having a layered structure represented by Chemical Formula 1 below. [Chemical formula 1] Li a1 Ni x1 Co y1 Mn z1 B1 c1 O 2-b1

[0084] In Chemical Formula 1, 0.8≦a1≦1.2, 0.5≦x1≦0.8, 0≦y1≦0.3, 0.1≦z1≦0.5, 0≦c1≦0.1, 0≦b1≦0.05, and x1+y1+z1+c1=1. For example, c1 can be 0.005.

[0085] B1 may be a dopant doped into the first particle PTC1. B1 may include at least one selected from the group consisting of Ti, Mg, V, Nb, and Al. For example, B1 may be Al.

[0086] Referring again to FIG. 8, as another example, the first particles PTC1 may have a polycrystalline form and include secondary particles formed by agglomeration of at least two or more primary particles NNP. In other words, one first particle PTC1 may include a plurality of primary particles NNP agglomerated together. The first particles PTC1 formed by a plurality of primary particles NNP may be irregular. For example, the first particles PTC1 formed by a plurality of primary particles NNP may have a spherical or elliptical shape. In this specification, the first particles PTC1, which are secondary particles, may be defined as large-grain PC.

[0087] In one embodiment, the average particle size (D50) may refer to the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. The average particle size (D50) of the first particles PTC1, which are secondary particles, may be a value measured using a particle size analyzer. Therefore, the average particle size (D50) of the secondary particles may be 10 μm to 25 μm, or 12 μm to 18 μm.

[0088] The particle size of the primary NNP particles may be 8 μm or less. For example, the particle size of the primary NNP particles may be 2 μm to 8 μm, or 4 μm to 5 μm. In one embodiment, the particle size may refer to the diameter measured by randomly selecting about 30 primary NNP particles from an electron microscope photograph of the positive electrode active material. The particle size of the primary NNP particles may be uniform.

[0089] In the present invention, the first particles PTC1 may be present in small particles SP (see FIG. 7) or large particles PC (see FIG. 8). Also, the first particles PTC1 may be a positive electrode active material including small particles SP and large particles PC.

[0090] In this specification, the small particles SP and the large particles PC may be interpreted as meaning the first particles PTC1. Also, the first particles PTC1 may be interpreted as including the small particles SP and the large particles PC.

[0091] 9 again, in this specification, when the first particles PTC1 coexist in the form of small particles SP and large particles PC, or when the first particles PTC1 coexist in the form of large particles PC and small particles SP in the positive electrode active material, it can be said to be bimodal. That is, the first particles PTC1 can include both single particles and secondary particles.

[0092] The BET specific surface area of ​​the first particles PTC1 may be small. The specific surface area of ​​the first particles PTC1 may be smaller than the specific surface area of ​​the second particles PTC2. For example, the BET specific surface area of ​​the first particles PTC1 is 0.8 m 2 / g~1.2m 2 Therefore, by mixing with a nano-sized olivine compound, a small amount of binder can be used.

[0093] 2nd particle PTC2 Referring again to FIG. 10, the second particles PTC2 may have a single particle shape. In this specification, a single particle may refer to a single particle without an internal grain boundary. A single particle may refer to a single particle, a monolith structure, a single structure, or a non-aggregated particle, in which particles morphologically exist in an independent phase without aggregation. For example, a single particle may be a single crystal. Alternatively, a single particle may contain several crystals. A single particle may be in a singly separated form. Alternatively, a single particle may be in a form in which two to one hundred single particles are attached to each other. That is, the second particles PTC2 may be provided in various sizes. For example, the average particle size of the second particles PTC2 may be about 1 μm. The minimum particle size of the second particles PTC2 may be 20 nm to 500 nm, or 200 nm to 300 nm. For example, the minimum particle size may refer to the diameter measured by randomly selecting about 30 primary particles from an electron microscope photograph of the positive electrode active material.

[0094] The average particle size (D50) of the second particles PTC2 may be 100 nm to 2 μm, or 500 nm to 2 μm. For example, the average particle size of the second particles PTC2 may be approximately 1 μm. In one embodiment, the average particle size may be measured using a particle size analyzer. The average particle size may refer to the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution.

[0095] The second particles PTC2 may include an olivine structure compound represented by the following Chemical Formula 2. [Chemical formula 2] Li a2 Mn x2 Fe y2 B2 z2 PO 4-b2

[0096] In Formula 2, 0.8≦a2≦1.2, 0.4≦x2≦0.8, 0≦y2≦0.6, 0≦z2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1. For example, z2 can be 0.002.

[0097] B2 may be a dopant doped into the second particles PTC2. B2 may include at least one selected from the group consisting of Al, Ti, V, and Mg. B2 controls the size of the primary particles to be uniform, and can improve the charge / discharge efficiency, low-temperature characteristics, and life characteristics of the lithium secondary battery.

[0098] In one embodiment, the second particles PTC2 may include a coating layer on their surfaces. The coating layer may cover the entire surface of the second particles PTC2 or a portion of the surface of the second particles PTC2. For example, the coating layer may include carbon and / or a carbon-containing compound. The coating layer may improve the structural stability of the second particles PTC2 and may improve electrical conductivity.

[0099] The coating layer may further include at least one selected from the group consisting of a titanium-containing compound, a magnesium-containing compound, and a vanadium-containing compound. Metal-containing compounds, such as titanium-containing compounds, magnesium-containing compounds, and vanadium-containing compounds, may be, for example, metal oxides, metal hydroxides, metal carbonates, composites thereof, or mixtures thereof. The metal-containing compounds may further include other metals or non-metal elements. For example, the metal-containing compounds may further include lithium.

[0100] The second particles PTC2 may further contain carbon derived from the coating layer. The carbon element content in the second particles PTC2 may be 0.5 wt % to 10 wt %, 1 wt % to 3 wt %, or 1.5 wt % to 2.5 wt %.

[0101] The BET specific surface area of ​​the second particles PTC2 may be large. For example, the BET specific surface area of ​​the second particles PTC2 is 10 m 2 / g~30m 2 For example, the BET specific surface area of ​​the second particles PTC2 may be 20 m 2 / g.

[0102] According to the comparative example of the present invention shown in FIG. 11, the positive electrode active material layer AML1 may include a nano-shaped positive electrode active material. The nano-shaped positive electrode active material may include an olivine-based compound and nano-sized particles NP. For example, the chemical formula of the olivine-based compound may be expressed as Chemical Formula 2. For example, the nano-shaped positive electrode active material may be composed of nano-sized particles NP that are not spherical. That is, the nano-shaped positive electrode active material may have a random shape. The nano-shaped positive electrode active material may be provided in various sizes. For example, the average particle size of the nano-shaped positive electrode active material may be 500 nm to 2.5 μm, or about 1 μm. The minimum particle size of the nano-shaped positive electrode active material may be 100 nm to 500 nm, or 200 nm to 300 nm. In one embodiment, the average particle size may be measured using a particle size analyzer. The average particle size (D50) may refer to the diameter of particles whose cumulative volume is 50% by volume in the particle size distribution. For example, the minimum particle size may refer to the diameter measured by randomly selecting approximately 30 primary particles from an electron microscope image of the nano-type positive electrode active material. The nano-type positive electrode active material may have a porosity of greater than 40%. The Span value of the nano-type positive electrode active material, as analyzed by a particle size analyzer, may be outside the range of 0.3 to 0.75.

[0103] Referring again to Figure 10, the second active material layer ATL2 of the present invention can include second particles PTC2. The second particles PTC2 are a lithium iron phosphate compound with an olivine structure, which is very stable and has high chemical stability. While the second particles PTC2 have excellent lifespan characteristics due to their stable structure compared to other positive electrode materials, they are subject to degradation of lifespan characteristics when used at high voltages, limiting the operating voltage. The second particles PTC2 contain manganese (Mn), which improves high-voltage characteristics and energy density compared to typical lithium iron phosphate compounds.

[0104] If the particle size is too small, the binding strength between the current collector and the positive electrode active material is weak, making it difficult to process the electrode plate and potentially requiring a large amount of binder (see Figure 11).

[0105] 6 to 10, by inserting the first active material layer ATL1 between the current collector COL1 and the second active material layer ATL2 and mixing the first particles PTC1 and the second particles PTC2 in an appropriate ratio, the electrode plate binding strength can be improved and the binder BND content can be reduced. In addition, by mixing them, the capacity, density characteristics, high-temperature stability, and life characteristics can be improved.

[0106] The weight ratio of the first particles PTC1 and the second particles PTC2 contained in the first and second active material layers ATL1 and ATL2 may be 10:90 to 30:70. For example, the weight ratio of the first particles PTC1 and the second particles PTC2 contained in the first and second active material layers ATL1 and ATL2 may be 15:85 to 30:70, 20:80 to 30:70, or 30:70.

[0107] If the weight ratio of the first particles PTC1 to the second particles PTC2 satisfies the described range, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 can be improved. Therefore, a lithium secondary battery with reduced resistance can be provided. Furthermore, if the weight ratio of the first particles PTC1 to the second particles PTC2 satisfies the described range, a lithium secondary battery with excellent performance can be provided.

[0108] The total doping amount of Mn may be 0.49 to 0.53. For example, the total doping amount of Mn may be 0.51. The "total doping amount of Mn (A+B)" may be defined as the sum of the doping amount of Mn contained in the first active material layer ATL1 (A) and the doping amount of Mn contained in the second active material layer ATL2 (B). The doping amount of Mn contained in the first active material layer ATL1 (A) may be defined as the product of the doping amount of Mn in the first particles PTC1 (z1 in Formula 1) and the weight ratio of the first particles PTC1 described above. The doping amount of Mn contained in the second active material layer ATL2 (B) may be defined as the product of the doping amount of Mn in the second particles PTC2 (x2 in Formula 2) and the weight ratio of the second particles PTC2 described above.

[0109] If the total doping amount of Mn satisfies the above-described range, the binding strength of the positive electrode active material layer AML1 to the current collector COL1 can be improved. Therefore, a lithium secondary battery with reduced resistance and excellent performance can be provided.

[0110] The positive electrode for a lithium secondary battery according to an embodiment of the present invention has the following effects.

[0111] A relatively large amount of binder BND is required to adhere nano-sized particles NP (see FIG. 11) with a small average particle size to current collector COL1 (see FIG. 1), while a relatively small amount of first binder BND1 is required to fix first particles PTC1 with a small BET specific surface area and a large average particle size to current collector COL1 (see FIG. 1). The positive electrode active material layer AML1 of the present invention includes a first active material layer ATL1 containing first particles PTC1, which improves the binding strength to the current collector while containing a large amount of nano-sized olivine-based compounds, thereby facilitating the manufacture of an electrode plate and reducing the electrode plate resistance. Furthermore, a lithium secondary battery with excellent capacity and life characteristics and high operating voltage and energy density can be provided.

[0112] The present invention will be described in more detail with reference to the following examples, but these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0113] Production Example 1: Production of small NCM particles The small particle precursor was manufactured using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 60:10:30 to prepare a metal raw material mixture. The metal raw material mixture, ammonia water, 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 particle precursor (NiSO4·6H2O) with an average particle size of approximately 4 μm. 0.6 Co 0.1 Mn 0.3 (OH)2) powder was obtained.

[0114] The small-particle precursor and anhydrous lithium hydroxide (LiOH) were dry-mixed using a Henschel mixer. Lithium and transition metals were mixed in a molar ratio of approximately 1.05:1. The transition metals were the sum of the transition metals (Ni + Co + Mn) contained in the mid-nickel precursor. A melting agent was then added to the mixture, and the mixture was heat-treated (i.e., calcined) in an oxygen atmosphere at approximately 910°C for 8 hours to synthesize small-particle lithium composite oxide particles. The particles were then pulverized in a jet mill at a pressure of 3 bar.

[0115] After adding aluminum oxide to the oxide, a second heat treatment was carried out at 800°C for 8 hours in an oxygen atmosphere to produce small NCM particles. The chemical formula of the small NCM particles is LiNi 0.6 Co 0.1 Mn 0.3 It was O2.

[0116] Production Example 2: Production of large NCM particles The large-particle precursor was manufactured using the coprecipitation method. Specifically, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 60:10:30 to prepare a metal source mixture. To form a complex compound, a dilute solution of ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant. The metal source mixture, ammonia water, and sodium hydroxide were then added to a reactor. The sodium hydroxide was added to maintain the pH of the mixture in the reactor. The reaction was carried out for approximately 20 hours while stirring the mixture in the reactor. 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 large-particle precursor (NiSO4·6H2O) with an average particle size of approximately 14 μm. 0.6 Co 0.1 Mn 0.3 (OH)2) powder was obtained.

[0117] The large-particle precursor and anhydrous lithium hydroxide (LiOH) were dry mixed using a Henschel mixer. Lithium and transition metals were mixed in a molar ratio of approximately 1.05:1. The transition metals were the sum of the transition metals contained in the large-particle precursor (Ni + Co + Mn). The mixture was heat-treated (i.e., calcined) in an oxygen atmosphere at approximately 850°C for 15 hours to synthesize large-particle lithium composite oxide particles. The particles were then pulverized in a jet mill at a pressure of 3 bar.

[0118] After adding aluminum oxide to the oxide, a second heat treatment was carried out at 800°C for 8 hours in an oxygen atmosphere to produce large NCM particles. The chemical formula of the large NCM particles is LiNi 0.6 Co 0.1 Mn 0.3 It was O2.

[0119] Manufacturing Example 3: Manufacturing of bimodal NCM The small lithium composite oxide particles of Production Example 1 and the large lithium composite oxide particles of Production Example 2 were mixed in a weight ratio of 70:30 to prepare bimodal particles.

[0120] Production Example 4: Production of LMFP particles in single particle form Mn 0.6 Fe 0.4 Manganese iron phosphate precursor (PO4), lithium carbonate, magnesium dioxide, and titanium dioxide were added to water in a molar ratio of 1:1.03:0.01:0.004. 10 wt% glucose was added to the mixture. The mixture was subjected to a wet grinding process using a ball mill. The mixture was evaporated to dryness in a heating oven tray and then placed 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 product was pulverized at a rotation speed of 8000 rpm to obtain single-particle olivine-based compound particles. The chemical formula of the olivine-based compound particles is LiMn 0.6 Fe 0.4 It was PO4.

[0121] Example 1: Fabrication of a positive electrode including a first active material layer and a second active material layer A first active material slurry was prepared by dispersing bimodal NCM particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.976:0.012:0.012.

[0122] A second active material slurry was prepared by dispersing single particle LMFP particles, a second binder (polyvinylidene fluoride), and a second conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.94:0.03:0.03.

[0123] The first active material slurry was applied to a 15 μm-thick aluminum (Al) thin film current collector and dried to form a first active material layer. The second active material slurry was applied to the first active material layer and dried to form a second active material layer. The first and second active material layers were formed so that the weight ratio of the bimodal NCM in the first active material layer to the single-particle LMFP particles in the second active material layer was 30:70. A roll press was performed to fabricate a positive electrode in which the aluminum current collector, first active material layer, and second active material layer were stacked in order. The thickness ratio of the first active material layer to the second active material layer was 3:7.

[0124] Example 2: Fabrication of a positive electrode including a first active material layer and a second active material layer The first active material slurry was prepared in the same manner as in Example 1, except that the first active material slurry was prepared by dispersing small NCM particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone in a weight ratio of 0.976:0.012:0.012.

[0125] Example 3: Fabrication of a positive electrode including a first active material layer and a second active material layer The first active material slurry was prepared in the same manner as in Example 1, except that the large NCM particles, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 0.976:0.012:0.012.

[0126] Comparative Example 1: Preparation of a positive electrode containing one active material layer A first active material slurry was prepared by dispersing small NCM particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.976:0.012:0.012. The first active material slurry was applied to a 15 μm-thick aluminum (Al) thin film current collector and dried to form a first active material layer. A roll press was performed to prepare a positive electrode in which the aluminum current collector and the first active material layer were stacked in order.

[0127] Comparative Example 2: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that the first active material slurry was prepared by dispersing single-particle LMFP particles, a first binder (polyvinylidene fluoride), and a first conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.94:0.03:0.03.

[0128] Comparative Example 3: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that small NCM particles and single-particle LMFP particles were mixed in a weight ratio of 70:30 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0129] Comparative Example 4: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that small NCM particles and single-particle LMFP particles were mixed in a weight ratio of 60:40 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0130] Comparative Example 5: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that small NCM particles and single-particle LMFP particles were mixed in a weight ratio of 50:50, and a first binder (polyvinylidene fluoride) and a first conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 0.48:0.48:0.02:0.02.

[0131] Comparative Example 6: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that small NCM particles and single-particle LMFP particles were mixed in a weight ratio of 40:60 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0132] Comparative Example 7: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that small NCM particles and single-particle LMFP particles were mixed in a weight ratio of 30:70 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0133] Comparative Example 8: Production of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that small NCM particles and single-particle LMFP particles were mixed in a weight ratio of 20:80 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0134] Comparative Example 9: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that small NCM particles and single-particle LMFP particles were mixed in a weight ratio of 10:90 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0135] Comparative Example 10: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that the large NCM particles, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 0.976:0.012:0.012.

[0136] Comparative Example 11: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that large NCM particles and single-particle LMFP particles were mixed in a weight ratio of 30:70 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0137] Comparative Example 12: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that the bimodal NCM particles, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) were dispersed in N-methylpyrrolidone in a weight ratio of 0.976:0.012:0.012 to prepare the first active material slurry.

[0138] Comparative Example 13: Preparation of a positive electrode containing one active material layer The first active material slurry was prepared in the same manner as in Comparative Example 1, except that bimodal NCM particles and single-particle LMFP particles were mixed in a weight ratio of 30:70 and dispersed in N-methylpyrrolidone together with a first binder (polyvinylidene fluoride) and a first conductive material (carbon black).

[0139] Comparative Example 14: Production of a positive electrode including a first active material layer and a second active material layer A positive electrode with FAD2 / FAD1=0.83 was produced.

[0140] The same method as in Example 1 was used to prepare the first active material slurry, except that the bimodal NCM particles, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) were dispersed in N-methylpyrrolidone at a weight ratio of 0.976:0.012:0.012 to prepare the first active material slurry, and the single particle LMFP particles, the second binder (polyvinylidene fluoride), and the second conductive material (carbon black) were dispersed in N-methylpyrrolidone at a weight ratio of 0.98:0.01:0.01 to prepare the second active material slurry.

[0141] Comparative Example 15: Production of a positive electrode including a first active material layer and a second active material layer A positive electrode with FAD2 / FAD1=3.33 was produced.

[0142] The same method as in Example 1 was used to prepare the first active material slurry, except that the bimodal NCM particles, the first binder (polyvinylidene fluoride), and the first conductive material (carbon black) were dispersed in N-methylpyrrolidone at a weight ratio of 0.976:0.012:0.012, and the second active material slurry was prepared by dispersing the single-particle LMFP particles, the second binder (polyvinylidene fluoride), and the second conductive material (carbon black) in N-methylpyrrolidone at a weight ratio of 0.92:0.04:0.04.

[0143] Lithium secondary battery manufacturing A 2032-type coin half-cell was fabricated using the prepared positive electrode and a lithium metal counter electrode as the counter electrode. A separator (approximately 16 μm thick) made of porous polyethylene (PE) film was placed between the positive electrode and the lithium metal counter electrode, and an electrolyte solution was injected to fabricate a lithium secondary battery. The electrolyte used was a mixture of 1.3 M LiPF6 with a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylene carbonate (DMC) in a volume ratio of 3:4:3.

[0144] [Table 1]

[0145] [Table 2]

[0146] Evaluation example 1: Analysis of the surface of the positive electrode active material SEM images of the first particles and second particles prepared in Preparation Examples 1 and 4 are shown in Figures 12 and 13, respectively. Referring to Figure 12, it can be seen that the first particles prepared in Preparation Example 1 of the present invention are in the form of micro-sized single particles. Referring to Figure 13, it can be seen that the second particles prepared in Preparation Example 4 of the present invention are in the form of nano-sized fine single particles.

[0147] Evaluation example 2: Active material evaluation The pellet density (PD) of the positive electrode active materials of the Examples and Comparative Examples was measured, and the results are shown in Table 3.

[0148] [Table 3]

[0149] Evaluation example 3: Resistance and adhesion evaluation The characteristics of the lithium secondary batteries prepared using the positive electrode active materials of the Examples and Comparative Examples were evaluated.

[0150] To determine the initial charge capacity and initial discharge capacity, the lithium secondary battery was initially charged at 25°C under constant current (0.2C) and constant voltage (4.45V) conditions (cutoff 0.05C), rested for 10 minutes, and then discharged at a constant current (0.2C) to 3.0V. The initial charge capacity and initial discharge capacity were measured and the efficiency was calculated. The lithium secondary battery was charged to SOC50 at a constant current of 0.2C and left at SOC50 for 1 hour. The lithium secondary battery was then discharged at 1.0C for 10 seconds and left for another 10 seconds. At this point, the difference between the voltage after discharge and the voltage after a 10-second rest was divided by the current to calculate the cell resistance (DC-IR). The results are shown in Table 4 below.

[0151] [Table 4]

[0152] Referring to Table 4, the lithium secondary batteries including the positive electrodes according to Examples 1 to 3 had higher discharge capacities and lower resistances compared to Comparative Examples 2, 7, 11, and 13. This indicates that the binding strength of the positive electrode including the olivine-based compound can be increased by introducing a first active material layer including the first particles.

[0153] Evaluation example 4: Battery characteristic evaluation The characteristics of the lithium secondary batteries prepared using the positive electrode active materials of the Examples and Comparative Examples were evaluated.

[0154] The lithium secondary battery was initially charged at 25°C under constant current (0.2C) and constant voltage (4.45V) (cutoff 0.05C), rested for 10 minutes, and then discharged at a constant current (0.2C) until the battery reached 3.0V. The average voltage and energy density were evaluated. The battery was then charged and discharged 50 times at 1.0C / 1.0C at 45°C. An additional coin cell was fabricated and initially charged at a constant current (0.2C) and constant voltage (4.45V) (cutoff 0.05C), rested for 10 minutes, and then discharged at a constant current (0.2C) until the battery reached 3.0V. The battery was then charged again, and the discharge capacity was measured at -20°C. The battery characteristics were summarized in Table 5 below.

[0155] [Table 5]

[0156] Referring to Tables 4 and 5, it was confirmed that the lithium secondary batteries including the positive electrodes according to Examples 1 to 3 had excellent capacity and life characteristics, as well as high operating voltage and energy density.

[0157] Although the present invention has been described above with reference to the accompanying drawings, it should be understood that the present invention may be embodied in other specific forms without changing the technical spirit or essential features thereof. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting. [Explanation of symbols]

[0158] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. A current collector; a first active material layer on the current collector, the first active material layer including first particles, a first binder, and a first conductive material; a second active material layer on the first active material layer, the second active material layer including second particles, a second binder, and a second conductive material; The first particles include a layered structural compound represented by the following Chemical Formula 1: The second particles include an olivine structure compound represented by the following Chemical Formula 2: the second particle is a single particle, the first binder and the first conductive material constitute a first functional additive; the second binder and the second conductive material constitute a second functional additive; a weight ratio of the first functional additive in the first active material layer being smaller than a weight ratio of the second functional additive in the second active material layer; Positive electrode for lithium secondary batteries. [Chemical formula 1] Li a1 Ni x1 Co y1 Mn z1 B1 c1 O 2-b1 In the formula 1, 0.8≦a1≦1.2, 0.5≦x1≦0.8, 0≦y1≦0.3, 0.1≦z1≦0.5, 0≦c1≦0.1, 0≦b1≦0.05, and x1+y1+z1+c1=1; B1 includes at least one selected from the group consisting of Ti, Mg, V, Nb, and Al; [Chemical formula 2] Li a2 Mn x2 Fe y2 B2 z2 PO 4-b2 In the formula 2, 0.8≦a2≦1.2, 0.4≦x2≦0.8, 0≦y2≦0.6, 0≦z2≦0.05, 0≦b2≦0.05, and x2+y2+z2=1; B2 includes at least one selected from the group consisting of Al, Ti, V, and Mg.

2. The ratio of the weight ratio of the second functional additive to the weight ratio of the first functional additive is 1.5 to 3; The positive electrode for a lithium secondary battery according to claim 1 .

3. The content of the first binder is less than the content of the second binder; The positive electrode for a lithium secondary battery according to claim 1 .

4. The content of the first binder is 1.2 to 2 parts by weight based on 100 parts by weight of the first active material layer, The content of the second binder is 2 to 3 parts by weight based on 100 parts by weight of the second active material layer. The positive electrode for a lithium secondary battery according to claim 1 .

5. The content of the first conductive material is less than the content of the second conductive material. The positive electrode for a lithium secondary battery according to claim 1 .

6. The content of the first conductive material is 1.2 to 2 parts by weight based on 100 parts by weight of the first active material layer, The content of the second conductive material is 2 to 3 parts by weight based on 100 parts by weight of the second active material layer. The positive electrode for a lithium secondary battery according to claim 1 .

7. a weight ratio of the first particles to the second particles contained in the first active material layer and the second active material layer is 10:90 to 30:70; The positive electrode for a lithium secondary battery according to claim 1 .

8. a total doping amount of the Mn contained in the first active material layer and the second active material layer is 0.49 to 0.53; The positive electrode for a lithium secondary battery according to claim 1 .

9. the first particles are single crystals; The positive electrode for a lithium secondary battery according to claim 1 .

10. the first particle is a single particle, The first particles have an average particle size of 3 μm to 10 μm. The positive electrode for a lithium secondary battery according to claim 1 .

11. the first particles have a secondary particle shape composed of a plurality of primary particles, The first particles have an average particle size of 10 μm to 25 μm, The average particle size of the primary particles is 8 μm or less. The positive electrode for a lithium secondary battery according to claim 1 .

12. The first particles include single particles and secondary particles. The positive electrode for a lithium secondary battery according to claim 1 .

13. The BET specific surface area of ​​the first particles is 0.8 m 2 / g to 1.2m 2 / g, The positive electrode for a lithium secondary battery according to claim 1 .

14. The average particle size of the second particles is 100 nm to 2 μm. The positive electrode for a lithium secondary battery according to claim 1 .

15. the second particles include a coating layer containing carbon; The carbon content in the second particles is 1.5% by weight to 2.5% by weight. The positive electrode for a lithium secondary battery according to claim 1 .

16. The BET specific surface area of ​​the second particles is 10 m ２ / g to 30m ２ / g, The positive electrode for a lithium secondary battery according to claim 1 .

17. The thickness of the first active material layer is smaller than the thickness of the second active material layer. The positive electrode for a lithium secondary battery according to claim 1 .

18. the first binder and the second binder each include at least one selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, an epoxy resin, a (meth)acrylic resin, a polyester resin, and nylon; The positive electrode for a lithium secondary battery according to claim 1 .

19. The first conductive material and the second conductive material each include at least one selected from the group consisting of a carbon-based material, a metal-based material, and a conductive polymer. The positive electrode for a lithium secondary battery according to claim 1 .

20. A lithium secondary battery comprising the positive electrode according to claim 1.

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