Positive electrode active material for lithium secondary battery and lithium secondary battery containing the same

Abstract

To provide a positive electrode active material for lithium secondary batteries, which has a high energy density and improved lifetime characteristics.SOLUTION: The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery including the positive electrode. More specifically, the positive electrode active material includes first particles including a first lithium composite oxide having a spinel crystal structure, second particles including a second lithium composite oxide having a layered crystal structure, and third particles including a third lithium composite oxide having a layered crystal structure, an average particle diameter of the second particles being greater than an average particle diameter of the third particles. Each of the first, second and third particles have a first, second and third weight ratio respectively relative to a total weight of the first, second, and third particles, the first weight ratio being greater than a sum of the second weight ratio and the third weight ratio.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material, a method for producing the same, a positive electrode containing the same, and a lithium secondary battery containing the positive electrode. [Background technology]

[0002] Batteries generate electrical energy through physical and chemical reactions of materials and supply power to the outside world. They are used in living environments where we are surrounded by various electrical and electronic devices, when AC power cannot be obtained from the building or when DC power is required.

[0003] Among these batteries, primary batteries and secondary batteries, which are chemical batteries that utilize chemical reactions, are commonly used. Primary batteries, commonly known as dry batteries, are consumable batteries. On the other hand, secondary batteries are rechargeable batteries that can undergo repeated oxidation / reduction processes at the positive and negative electrodes. When a reduction reaction occurs at the positive electrode due to electric current, the battery is charged, and when an oxidation reaction occurs at the positive electrode, the battery is discharged. Secondary batteries undergo this charge-discharge cycle repeatedly.

[0004] In lithium secondary batteries, positive electrode active materials made of lithium composite oxides containing a high content of nickel have been attracting attention. While these positive electrode active materials have high energy density, there is a problem in that the battery life and stability are rapidly reduced as the nickel content increases. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a positive electrode active material for a lithium secondary battery having high energy density and improved life characteristics.

[0006] Another object of the present invention is to provide a lithium secondary battery having excellent output, life span, and capacity retention characteristics. [Means for solving the problem]

[0007] A cathode active material according to the present invention may include first particles including a first lithium composite oxide having a spinel crystal structure, second particles including a second lithium composite oxide having a layered crystal structure, and third particles including a third lithium composite oxide having a layered crystal structure. The first particles may have a first weight ratio relative to the total weight of the first to third particles, the second particles may have a second weight ratio relative to the total weight, and the third particles may have a third weight ratio relative to the total weight, and the first weight ratio may be greater than the sum of the second weight ratio and the third weight ratio.

[0008] According to another aspect of the present invention, a positive electrode for a lithium secondary battery may include the above-described positive electrode active material.

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

[0010] In the positive electrode active material for a lithium secondary battery according to the present invention, the weight ratio of the first particles having a spinel crystal structure may be greater than the sum of the weight ratios of the second and third particles having a layered crystal structure.

[0011] Therefore, the cathode active material of the present invention can have high energy density and improved life characteristics, and a lithium secondary battery using the cathode active material of the present invention can have improved capacity characteristics and improved life characteristics. [Brief explanation of the drawings]

[0012] [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 diagram showing a positive electrode active material according to an embodiment of the present invention. [Figure 3] 1 is a cross-sectional view of a large-grain lithium composite oxide according to one embodiment of the present invention. [Figure 4]1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF 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 embodied in various forms and can be modified in various ways. The description of the present embodiments is provided merely to complete the disclosure of the present invention and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains.

[0014] 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.

[0015] The embodiments described herein are described with reference to cross-sectional views and / or plan views that are idealized examples of the present invention. In the drawings, thicknesses of films and regions are exaggerated for 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 intended to illustrate specific shapes of regions of a device and are not intended to limit the scope of the invention. In various embodiments of the present specification, terms such as "first," "second," and "third" are used to refer to various components, but these components should not be limited by such terms. These terms are merely used to distinguish one component from another. The embodiments described and illustrated herein also include complementary embodiments thereof.

[0016] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless otherwise specified in the phrase. When used in this specification, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components to the referenced components.

[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 100, a negative electrode 200, an electrolyte 300, and a separator 400.

[0018] The positive electrode 100 and the negative electrode 200 may be separated from each other by a separator 400. The separator 400 may be disposed between the positive electrode 100 and the negative electrode 200. The positive electrode 100, the negative electrode 200, and the separator 400 may be in contact with an electrolyte 300. The positive electrode 100, the negative electrode 200, and the separator 400 may be impregnated in the electrolyte 300.

[0019] The electrolyte 300 may be a medium for transferring lithium ions between the positive electrode 100 and the negative electrode 200. In the electrolyte 300, the lithium ions may pass through the separator 400 and move toward the positive electrode 100 or the negative electrode 200.

[0020] The positive electrode 100 may include a first current collector COL1 and a positive electrode active material layer AML1 on the first current collector COL1. The first current collector COL1 may include a metal selected from the group consisting of aluminum, copper, nickel-plated copper, stainless steel, nickel, titanium, palladium, and an aluminum-cadmium alloy. The first current collector COL1 may have a shape such as a film, sheet, foil, mesh, net, porous material, foam, or nonwoven fabric.

[0021] The positive electrode active material layer AML1 may include a binder, a conductive material, and a positive electrode active material. The positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 98 wt%, based on the total weight of the positive electrode active material layer AML1. The positive electrode active material may be a source of lithium ions. The positive electrode active material may be a lithium transition metal oxide that further includes at least one transition metal in addition to lithium. A detailed description of positive electrode active materials according to embodiments of the present invention will be provided below with reference to FIGS. 2 and 3.

[0022] The conductive material can impart conductivity to the positive electrode active material layer AML1. The conductive material can include at least one of a carbon-based material (e.g., graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, or carbon fiber), metal powder, metal fiber, conductive whisker, conductive metal oxide, conductive polymer, and combinations thereof. The conductive material can be included in an amount of 1 wt % to 30 wt % based on the total weight of the positive electrode active material layer AML1.

[0023] The binder can improve adhesion between the positive electrode active material and the first current collector COL1. For example, the binder can include at least one of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and combinations thereof. The binder can be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer AML1.

[0024] The negative electrode 200 may include a second current collector COL2 and a negative electrode active material layer AML2 on the second current collector COL2. The second current collector COL2 may be the same as or similar to the first current collector COL1 described above. The second current collector COL2 may be the same as the first current collector COL1 or may include a different metal. The second current collector COL2 may be the same as the first current collector COL1 or may have a different shape.

[0025] The negative electrode active material layer AML2 may include a binder, a conductive material, and a negative electrode active material. The binder and conductive material may be the same as those described above for the positive electrode active material layer AML1. The negative electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 98 wt%, based on the total weight of the negative electrode active material layer AML2. The negative electrode active material may include at least one selected from the group consisting of a carbon material, lithium metal or a lithium metal compound, silicon or a silicon compound, and tin or a tin compound. Metal oxides such as TiO2 and SnO2 having a potential of less than 2 V may also be used as the negative electrode active material. The carbon material may include low-crystalline carbon and / or high-crystalline carbon.

[0026] Separator 400 may include a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. Separator 400 may include a single porous polymer film or a laminate of multiple porous polymer films. In another embodiment of the present invention, separator 400 may include a conventional porous nonwoven fabric, such as a high-melting point glass fiber or polyethylene terephthalate fiber.

[0027] Electrolyte 300 is A + B - It is possible to include salts having the following structure: + Li + , Na + , and K +It may contain at least one alkali metal cation selected from the group consisting of: - is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , BC4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 -- , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - 、 CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The compound may include at least one anion selected from the group consisting of:

[0028] In one embodiment of the present invention, the electrolyte 300 may be dissolved in an organic solvent, such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone, or a mixture thereof.

[0029] The case of the secondary battery according to the embodiment of the present invention may be adopted based on a conventional shape in the art, and may have any shape depending on the intended use of the battery, such as a cylindrical shape, a rectangular shape, a pouch shape, or a coin shape.

[0030] 2 is a diagram illustrating a positive electrode active material according to an embodiment of the present invention. Referring to FIG. 2, a positive electrode active material layer may include a plurality of first particles PTC1, a plurality of second particles PTC2, and a plurality of third particles PTC3.

[0031] The first particles PTC1 may have a first average particle size APD1. The second particles PTC2 may have a second average particle size APD2, and the third particles PTC3 may have a third average particle size APD3. The third average particle size APD3 may be smaller than the second average particle size APD2. The third average particle size APD3 may be smaller than the first average particle size APD1. The first average particle size APD1 may be larger or smaller than the second average particle size APD2.

[0032] The first average particle size may be 1.0 μm to 10.0 μm. The second average particle size APD2 may be 10.0 μm to 20.0 μm. The third average particle size APD3 may be 1.0 μm to 5.0 μm. As used herein, "average particle size," i.e., D50, refers to the particle size at which the volume cumulative percentage corresponds to 50% in the particle size distribution calculated from particle volume. For example, the average particle size can be measured using a particle size analyzer (PSA). In the present invention, the second particles PTC2 may be referred to as large particles, and the third particles PTC3 may be referred to as small particles.

[0033] 3 is a diagram showing secondary particles PTC2 according to an embodiment of the present invention. Referring to FIG. 3, the secondary particles PTC2 may have the shape of secondary particles (SDP) formed by agglomeration of a plurality of primary particles (PRP). The plurality of primary particles PRP may be arranged radially from the center to the surface of the secondary particles SDP.

[0034] Referring again to FIG. 2, the third particles PTC3 may have a granular or spherical shape. In one embodiment of the present invention, the third particles PTC3 may have a single particle shape. The single particle shape may include a primary particle shape or a secondary particle shape formed by the aggregation of several primary particles. The single particle shape may include one crystal grain or several crystal grains. A crystal grain may be the smallest unit in which the lithium composite oxide has one crystal direction. For example, the third particles PTC3 may include one primary particle and / or one single particle formed by the merging of several primary particles together.

[0035] Positive electrode active materials according to embodiments of the present invention may be bimodal, including large particles (e.g., PTC2) and small particles (e.g., PTC3) with different average particle sizes. The small particles fill the voids between the large particles, thereby improving the packing density of the positive electrode active material. Again, positive electrode active materials according to embodiments of the present invention may have a relatively high energy density per unit volume.

[0036] The first particle PTC1 can contain a first lithium composite oxide. The first lithium composite oxide can have a spinel crystal structure and can be represented by the following Chemical Formulas 1 to 3.

[0037] [Chemical Formula 1] Li a M2O4 In Chemical Formula 1, 1.0 ≦ a ≦ 1.1, and M can be manganese and one or more other elements selected from Group 4 to Group 13 elements.

[0038] [Chemical Formula 2] Li a Mn b M1 c M2 d O4 In Chemical Formula 2, 0.9 ≦ a ≦ 1.1, 0 < b ≦ 2.0, 0 ≦ c < 2.0, 0 ≦ d < 0.1, b + c + d = 2, M1 and M2 are different from each other, and each can be one selected from the group consisting of Co, Ni, V, Cr, Fe, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, and Pt.

[0039] [Chemical Formula 3] Li​​​​​​​​​​​​​​​​​​​​​M’O₂ In Chemical Formula 4, 0.9 ≤ a ≤ 1.1, M is one or more other elements selected from nickel and elements of Groups 4 to 13, and the nickel content in M’ can be 70 at% or more and less than 100 at%.

[0042] [Chemical Formula 5] Li a Ni b M₃ c M₄ d M₅ e O₂ In Chemical Formula 5, 0.9 ≤ a ≤ 1.1, 0.7 < b < 1.0, 0 < c < 0.3, 0 < d < 0.3, 0 ≤ e < 0.1, and b + c + d + e = 1. M₃, M₄, and M₅ are different from each other and each can be one selected from the group consisting of Mn, V, Cr, Fe, Co, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, and Pt.

[0043] [Chemical Formula 6] Li a Ni b Co c Mn d M₅ e O₂<00002​​​​​​​​​​​​In one embodiment, the weight ratio of the first particles PTC1 in the positive electrode active material may be 60 wt% to 90 wt%, 60 wt% to 80 wt%, or 70 wt% to 80 wt% of the total weight of the first to third particles PTC1, PTC2, and PTC3. The weight ratio of the second particles PTC2 may be 7 wt% to 30 wt%, or 10 wt% to 21 wt% of the total weight of the first to third particles PTC1, PTC2, and PTC3. The weight ratio of the third particles PTC3 may be 3 wt% to 12 wt%, or 3 wt% to 9 wt% of the total weight of the first to third particles PTC1, PTC2, and PTC3. When the first to third particles PTC1, PTC2, and PTC3 have such weight ratios, the output and life characteristics of a lithium secondary battery including the positive electrode active material may be improved.

[0046] The positive electrode active material has high structural stability because the first particles PTC1 account for 60 wt% to 90 wt% by weight. The positive electrode active material has high structural stability because it contains 10 wt% to 40 wt% of the second and third particles PTC2 and PTC3, which have a high nickel content and a layered crystal structure. The positive electrode active material has improved life and capacity characteristics compared to a material containing only the first particles PTC1.

[0047] Referring again to FIG. 2 , the positive electrode active material layer may further include a conductive material CDA dispersed among the first to third particles PTC1-PTC3. The conductive material CDA may be attached (or provided) on the surface of each of the first to third particles PTC1-PTC3. The density of the conductive material CDA on the first particles PTC1 may be greater than the density of the conductive material CDA on the second particles PTC2. The density of the conductive material CDA on the first particles PTC1 may be greater than the density of the conductive material CDA on the third particles PTC3. Again, the conductive material CDA may be more densely packed on the first particles PTC1 than on the second particles PTC2 and the third particles PTC3.

[0048] In the present invention, the density of the conductive material CDA can be defined as the amount of the conductive material CDA attached to the surface of the active material particle per unit surface area of ​​the active material particle. By further concentrating the conductive material around the particles with a spinel crystal structure that occupy a high mass ratio, the conductivity of the positive electrode active material layer AML according to the present invention can be improved.

[0049] The cathode 100 of FIG. 1 can be fabricated by a typical cathode fabrication method, except that the cathode active material according to an embodiment of the present invention is used. Specifically, a mixture can be prepared by dissolving or dispersing the cathode active material of the present invention, a binder, and a conductive material in a solvent. The binder and conductive material can be the same as those described above for the cathode active material layer AML1 of FIG. 1. The cathode 100 can be fabricated by applying the mixture to a first current collector COL1, drying it, and rolling it.

[0050] The solvent may be a solvent commonly used in the art, and may include, for example, at least one of dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, and combinations thereof.

[0051] 4 is a cross-sectional view schematically illustrating a lithium secondary battery according to one embodiment of the present invention. Referring to FIG. 4, the lithium secondary battery may include a positive electrode 100, a negative electrode 200, and a separator 400. The description of the positive electrode 100, the negative electrode 200, and the separator 400 in FIG. 4 may be substantially the same as that described above for the lithium secondary battery in FIG. 1.

[0052] The positive electrode 100, negative electrode 200, and separator 400 in FIG. 4 may be wound or folded to form an electrode assembly. The electrode assembly may be housed in a battery case 500. The electrode assembly may include multiple electrode assemblies. Separators 400 may be provided between the electrode assemblies. Stacked electrode assemblies may be provided in the battery case 500. The interior of the battery case 500 may be filled with an electrolyte (see 300 in FIG. 1). The battery case 500 may be sealed using a cap assembly 600. The battery case 500 according to an embodiment of the present invention may be cylindrical, prismatic, or pouch-shaped. The lithium secondary battery according to an embodiment of the present invention may be used in devices such as laptops, smartphones, or electric vehicles.

[0053] The present invention will be described in more detail with reference to the following examples. However, these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0054] Production Example 1: Production of first lithium composite oxide having a spinel crystal structure After dissolving 0.170g of MnSO4·H2O and 0.228g of (NH4)2S2O8 in 100ml of distilled water, sulfuric acid was added to adjust the pH to 1, and the reaction was carried out at 130℃ for 10 hours to obtain a solid precipitate. The obtained precipitate was washed several times with distilled water and dried at 300℃ for 3 hours to obtain solid MnO2 with an average particle size of 1μm.

[0055] Li2CO3 and the synthesized MnO2 were mixed so that the molar ratio of Li to Mn was 1:2, and heated at 600°C for 10 hours to synthesize LiMn2O4 particles with an average particle size of 1 μm.

[0056] Production Example 2: Production of large-grained lithium composite oxide having a layered crystal structure The large-particle precursor was prepared using the coprecipitation method. Nickel-based metal hydroxide (Ni 0.90 Co 0.07 Al 0.03 (OH)2) was prepared.

[0057] A metal source mixture was prepared by dissolving nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3·H2O) as raw materials for nickel-based metal hydroxides in a 90:7:3 molar ratio in distilled water as a solvent. To form a complex compound, a diluted ammonia water (NH4OH) solution and sodium hydroxide (NaOH) as a precipitant were prepared. The metal source mixture, ammonia water, and sodium hydroxide were then added to a reactor. 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.

[0058] The slurry in the reactor was filtered and washed with high-purity distilled water. The washed material was dried in a hot air oven at 190°C for 24 hours to obtain large-grain precursor (Ni) with a particle size of approximately 18 μm. 0.90 Co 0.07 Al 0.03 (OH)2) powder was obtained.

[0059] 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 1:1. The transition metals were the sum of the transition metals contained in the large-particle precursor (Ni+Co+Al). The mixture was heat-treated in an oxygen atmosphere at approximately 900°C for 10 hours (i.e., the first calcination step) to synthesize second particles, which are a second lithium composite oxide. The second particles were pulverized in a jet mill at a pressure of 3 bar.

[0060] Production Example 3: Production of large-grained lithium composite oxide having a layered crystal structure The small particle precursor was prepared using the coprecipitation method. Nickel-based metal hydroxide (Ni 0.90 Co 0.07 Mn 0.03 (OH)2) was prepared.

[0061] A metal raw material mixture was prepared by dissolving nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) as raw materials for nickel-based metal hydroxides in distilled water as a solvent in a molar ratio of 90:7:3. The metal raw material mixture, ammonia water, and sodium hydroxide were then placed in a reactor and reacted.

[0062] The slurry 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 small-grain precursor (Ni) particles with a particle size of approximately 3 μm. 0.90 Co 0.07 Mn 0.03 (OH)2) powder was obtained.

[0063] The small particle precursor and anhydrous lithium hydroxide (LiOH) were dry mixed using a Henschel mixer. Lithium and transition metal were mixed in a molar ratio of approximately 1:1. The transition metal was the sum of the transition metals contained in the small particle precursor (Ni + Co + Mn). The mixture was heat-treated in an oxygen atmosphere at approximately 750°C for 15 hours (i.e., the second calcination process) to synthesize third particles, which are a third lithium composite oxide. The third particles were then pulverized in a jet mill at a pressure of 3 bar.

[0064] Example 1: Preparation of composite positive electrode active material The first particles of Production Example 1, the second particles of Production Example 2, and the third particles of Production Example 3 were mixed in a weight ratio of 60:28:12 to obtain a composite positive electrode active material powder.

[0065] Example 2 The first particles of Preparation Example 1, the second particles of Preparation Example 2, and the third particles of Preparation Example 3 were mixed in a weight ratio of 70:21:9 to obtain a composite positive electrode active material powder.

[0066] Example 3 The first particles of Preparation Example 1, the second particles of Preparation Example 2, and the third particles of Preparation Example 3 were mixed in a weight ratio of 80:14:6 to obtain a composite positive electrode active material powder.

[0067] Example 4 The first particles of Preparation Example 1, the second particles of Preparation Example 2, and the third particles of Preparation Example 3 were mixed in a weight ratio of 90:7:3 to obtain a composite positive electrode active material powder.

[0068] Comparative Example 1 The first particles of Preparation Example 1, the second particles of Preparation Example 2, and the third particles of Preparation Example 3 were mixed in a weight ratio of 50:35:15 to obtain a composite positive electrode active material powder.

[0069] Comparative Example 2 The first particles of Preparation Example 1, the second particles of Preparation Example 2, and the third particles of Preparation Example 3 were mixed in a weight ratio of 95:3.5:1.5 to obtain a composite positive electrode active material powder.

[0070] Comparative Example 3 The positive electrode active material powder prepared using only the first particles of Preparation Example 1 was used.

[0071] Cathode manufacturing A positive electrode active material slurry was prepared by mixing 95 wt% of the final positive electrode active material, 3 wt% of polyvinylidene fluoride binder, and 2 wt% of carbon black conductive material in N-methylpyrrolidone solvent. The positive electrode active material slurry was applied to an aluminum current collector, dried, and then rolled to prepare a positive electrode.

[0072] Anode manufacturing Graphite, a binder, and a conductive material were mixed in N-methylpyrrolidone solvent to prepare a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper current collector, dried, and then rolled to prepare a negative electrode.

[0073] Lithium secondary battery manufacturing A coin-pull cell was fabricated using the prepared positive and negative electrodes. A polypropylene membrane (Celgard 3510) was used as the separator. The electrolyte used was a 1.3M LiPF6 solution mixed with a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and FEC (fluoroethylene carbonate) (volume ratio: 2:6:2).

[0074] Evaluation example 1: Life characteristics evaluation The life characteristics of the lithium secondary batteries prepared using the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated.

[0075] The lithium secondary battery was continuously charged and discharged up to 1000 cycles at 45°C under the condition of 0.5C charge and 0.5C discharge, and then the capacity retention rate after 1000 cycles was evaluated. The capacity retention rate was calculated using the following mathematical formula 1, and the evaluation results are shown in Table 1 below. [Mathematical formula 1] Capacity retention rate [%] = [discharge capacity at 1000th cycle / discharge capacity at 1st cycle] x 100

[0076] [Table 1]

[0077] Referring to Table 1, it can be seen that the lithium secondary battery according to the embodiment has a higher capacity retention rate than the lithium secondary battery according to the comparative example. That is, it can be seen that when the weight ratio of the first to third particles satisfies a certain range, an excellent capacity retention rate is exhibited.

[0078] Evaluation example 2: Resistance characteristic evaluation The resistance characteristics of the lithium secondary batteries fabricated using the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated.

[0079] The lithium secondary battery was continuously charged and discharged up to 1000 cycles at 45°C under the condition of 0.5C charge and 0.5C discharge, and the resistance increase rate after 1000 cycles was evaluated. The resistance increase rate was calculated using the following mathematical formula 2, and the evaluation results are shown in Table 2 below. [Mathematical formula 2] DC-IR increase rate [%] = [DC-IR at 1000th cycle (mΩ) / DC-IR at 1st cycle (mΩ)] x 100

[0080] [Table 2]

[0081] Referring to Table 2, it can be seen that the lithium secondary battery according to the embodiment exhibits a lower resistance increase rate than the lithium secondary battery according to the comparative example. That is, it can be seen that when the weight ratio of the first to third particles satisfies a certain range, the resistance increase is reduced. [Explanation of symbols]

[0082] 100 positive electrode 200 negative electrode 300 electrolytes 400 Separator

Claims

1. first particles including a first lithium composite oxide having a spinel crystal structure; second particles containing a second lithium composite oxide having a layered crystal structure; and third particles containing a third lithium composite oxide having a layered crystal structure, the average particle size of the second particles is larger than the average particle size of the third particles; the first particles have a first weight ratio relative to the total weight of the first to third particles; the second particles have a second weight ratio relative to the total weight; the third particles have a third weight ratio relative to the total weight; The positive electrode active material, wherein the first weight ratio is greater than the sum of the second weight ratio and the third weight ratio.

2. The cathode active material of claim 1 , wherein the average particle size of the second particles is 4 to 20 times the average particle size of the third particles.

3. The second particles include secondary particles including a plurality of primary particles, The positive electrode active material according to claim 1 , wherein the plurality of primary particles are arranged radially from the center to the surface of the second particle.

4. The first lithium composite oxide according to claim 1 is a positive electrode active material represented by the following Chemical Formula 1: [Chemical formula 1] Li a M 2 O 4 In the formula 1, 1.0≦a≦1.1; M is manganese and one or more other elements selected from among the Group 4 to Group 13 elements.

5. The first lithium composite oxide according to claim 1 is a positive electrode active material represented by the following chemical formula 2: [Chemical formula 2] Li a Mn b M11 c M2 d O 4 In the formula 2, 0.9≦a≦1.1, 0<b≦2.0, 0≦c<2.0, 0≦d<0.1, and b+c+d=2; M1 and M2 are different from each other and are each one selected from the group consisting of Co, Ni, V, Cr, Fe, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, and Pt.

6. The first lithium composite oxide according to claim 1 is a positive electrode active material represented by the following chemical formula 3: [Chemical formula 3] Li a Mn b Co c M2 d O 4 In the formula 3, 0.9≦a≦1.1, 0<b<2.0, 0<c<2.0, 0≦d<0.1, and b+c+d=2; M2 is one selected from the group consisting of V, Cr, Fe, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, and Pt.

7. The positive electrode active material of claim 1 , wherein the second lithium composite oxide and the third lithium composite oxide are each independently represented by the following Chemical Formula 4: [Chemical formula 4] Li a M'O 2 In the formula 4, 0.9≦a≦1.1; M' is nickel and one or more other elements selected from the group 4 to group 13 elements, and the nickel content in M' is 70 at % or more and less than 100 at %.

8. The positive electrode active material of claim 1 , wherein the second lithium composite oxide and the third lithium composite oxide are each independently represented by the following Chemical Formula 5: [Chemical formula 5] Li a N b M3 c M4 d M5 e O 2 In Formula 5, 0.9≦a≦1.1, 0.7<b<1.0, 0<c<0.3, 0<d<0.3, 0≦e<0.1, and b+c+d+e=1; M3, M4, and M5 are different from each other and are each one selected from the group consisting of Mn, V, Cr, Fe, Co, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, and Pt.

9. The positive electrode active material of claim 1 , wherein the second lithium composite oxide and the third lithium composite oxide are each independently represented by the following Chemical Formula 6: [Chemical formula 6] Li a Ni b Co c Mn d M5 e O 2 In Formula 6, 0.9≦a≦1.1, 0.7<b<1.0, 0<c<0.3, 0<d<0.3, 0≦e<0.1, and b+c+d+e=1; M5 is one selected from the group consisting of V, Cr, Fe, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, and Pt.

10. The positive electrode active material of claim 1 , wherein the second lithium composite oxide and the third lithium composite oxide are each independently represented by the following Chemical Formula 7: [Chemical formula 7] aLi 2 MnO 3 -(1-a)LiM’O 2 In the formula 7, 0<a<1; M' is two or more elements selected from the group consisting of Ni, Co, Mn, V, Cr, Fe, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, and Pt.

11. 2. The positive electrode active material of claim 1, wherein the first weight ratio is 60 wt% to 90 wt%.

12. The positive electrode active material of claim 11 , wherein the second weight ratio is greater than the third weight ratio.

13. The positive electrode active material of claim 11 , wherein the second weight ratio is 5 wt % to 30 wt %, and the third weight ratio is 3 wt % to 12 wt %.

14. A positive electrode for a lithium secondary battery, comprising the positive electrode active material according to claim 1.

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

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