Positive electrode active material for lithium secondary battery and lithium secondary battery

Abstract

To provide a positive electrode active material for a lithium secondary battery having high ion conductivity, and a lithium secondary battery whose stability and capacity retention characteristic are improved.SOLUTION: The present invention relates to a positive electrode active material and a manufacturing method for the same, a positive electrode including the same, and a lithium secondary battery including the positive electrode. More specifically, the positive electrode active material includes a first particle containing a first lithium complex oxide and having a first average particle diameter, and a second particle containing a second lithium complex oxide and having a second average particle diameter that is larger than the first average particle diameter. The first particle contains yttrium (Y) and zirconium (Zr) on its surface. Yttrium (Y) on the surface of the first particle has a first composition and yttrium (Y) on the surface of the second particle has a second composition. The ratio of the first composition to the second composition is more than 100.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a positive electrode active material, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery including the positive electrode.

Background Art

[0002] A battery that generates electrical energy through physical or chemical reactions of substances and supplies power externally is used when it is not possible to obtain an AC power supply supplied to a building or when a DC power supply is required, depending on the living environment surrounded by various electrical and electronic devices.

[0003] Among such secondary batteries, primary batteries and secondary batteries, which are chemical batteries using chemical reactions, are generally used. A primary battery is commonly referred to as a dry battery and is a consumable battery. On the other hand, a secondary battery is a rechargeable battery capable of repeating oxidation / reduction reactions at a positive electrode and a negative electrode.

[0004] In a lithium secondary battery, a positive electrode active material composed of a lithium composite oxide containing a high content of nickel has attracted attention. The positive electrode active material has the advantage of having a high energy density. Recently, for the purpose of increasing the capacity of lithium secondary batteries, a positive electrode active material in a bimodal form in which small particles and large particles having different average particle diameters are mixed is also used.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide a positive electrode active material for a lithium secondary battery having high ionic conductivity.

[0006] Another problem to be solved by the present invention is to provide a lithium secondary battery with improved stability and capacity maintenance characteristics.

Means for Solving the Problems

[0007] The positive electrode active material according to the concept of the present invention may include a first lithium composite oxide, first particles having a first average particle size, a second lithium composite oxide, and second particles having a second average particle size larger than the first average particle size. The first particles include yttrium (Y) and zirconium (Zr) on their surfaces. The yttrium (Y) on the surface of the first particles has a first composition, and the yttrium (Y) on the surface of the second particles has a second composition, but the ratio of the first composition to the second composition may be greater than 100.

[0008] A method for manufacturing a positive electrode active material according to another concept of the present invention may include synthesizing first particles including a first lithium composite oxide, the first particles having a first average particle size, synthesizing second particles including a second lithium composite oxide, the second particles having a second average particle size larger than the first average particle size, and mixing the first particles and the second particles. Synthesizing the first particles includes preparing a precursor of the first particles and firing the precursor together with a melting agent, and the melting agent may include yttrium (Y) and zirconium (Zr).

[0009] A positive electrode for a lithium secondary battery according to still another concept of the present invention may include the above-described positive electrode active material.

[0010] A lithium secondary battery according to yet another concept of the present invention may include the above-described positive electrode.

Advantages of the Invention

[0011] In the positive electrode active material for a lithium secondary battery according to the present invention, the small first particles may include yttrium (Y) and zirconium (Zr). And the small first particles may have a higher yttrium (Y) composition than the large second particles. Thereby, the positive electrode active material of the present invention may have high ionic conductivity. The lithium secondary battery using the positive electrode active material of the present invention may have improved output characteristics and capacity characteristics.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0013] In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention can be implemented in various forms without being limited to the embodiments disclosed below, and various modifications can be made. However, it is provided to make the disclosure of the present invention complete by the description of the present embodiment and to fully inform those having ordinary knowledge in the technical field to which the present invention pertains of the scope of the invention.

[0014] In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component or a third component can be interposed therebetween. Also, in the drawings, the thickness of the components is exaggerated for the effective explanation of the technical content. Throughout the specification, parts denoted by the same reference numerals indicate the same components.

[0015] The embodiments described in this specification are described with reference to cross-sectional views and / or plan views which are ideal exemplary diagrams of the present invention. In the drawings, the thickness of the film and the regions is exaggerated for the effective explanation of the technical content. Therefore, the regions illustrated in the drawings have schematic attributes, and the patterns of the regions illustrated in the drawings are for exemplifying the specific forms of the regions of the elements and not for limiting the scope of the invention. In various embodiments of this specification, terms such as first, second, third, etc. are used to describe various components, but these components should not be limited to such terms. These terms are merely used to distinguish one component from another. The embodiments described and exemplified herein include their complementary embodiments.

[0016] The terms used in this specification are for explaining the embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the context. The "comprises" and / or "comprising" used in the specification do not exclude the presence or addition of one or more other components of the recited component.

[0017] FIG. 1 is a conceptual diagram schematically showing 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 can be separated from each other with the separator 400 interposed therebetween. The separator 400 can be disposed between the positive electrode 100 and the negative electrode 200. The positive electrode 100, the negative electrode 200, and the separator 400 can be in contact with the electrolyte 300. The positive electrode 100, the negative electrode 200, and the separator 400 can be impregnated in the electrolyte 300.

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

[0020] The positive electrode 100 can 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 can include a metal selected from the group consisting of aluminum, copper, copper plated with nickel, stainless steel, nickel, titanium, palladium, and an aluminum-cadmium alloy. The first current collector COL1 can include a polymer substrate on at least one surface of which the metal is disposed (for example, coated, vapor deposited, etc.). The first current collector COL1 can have a form such as a film, a sheet, a foil, a mesh, a net, a porous body, a foam, or a non-woven fabric body.

[0021] The positive electrode active material layer AML1 can include a binder, a conductive material, and a positive electrode active material. The positive electrode active material can be contained in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 99 wt%, based on the total weight of the positive electrode active material layer AML1. The positive electrode active material can be a source of lithium ions. The positive electrode active material can be a lithium transition metal oxide and can further include at least one transition metal in addition to lithium. Specific descriptions of the positive electrode active material according to embodiments of the present invention will be described later with reference to FIG. 2.

[0022] The conductive material can impart conductivity to the positive electrode active material layer AML1. The conductive material may 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), a metal powder, a metal fiber, a conductive whisker, a conductive metal oxide, a conductive polymer, and combinations thereof. The conductive material may 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 the adhesion between the positive electrode active material and the first current collector COL1. For example, the binder may 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 may 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 description of the second current collector COL2 may be the same as or similar to that of the above - mentioned first current collector COL1. The second current collector COL2 may include the same or different metals as the first current collector COL1. The second current collector COL2 may have the same or different forms as the first current collector COL1.

[0025] The negative electrode active material layer AML2 may include a binder, a conductive material, and a negative electrode active material. The binder and the conductive material may be the same as those described above for the positive electrode active material layer AM1. The negative electrode active material may be contained in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 99 wt%, based on the total weight of the negative electrode active material layer AML2. The negative electrode active material may include at least one or more selected from the group consisting of a carbon material, a lithium metal or a lithium metal oxide, silicon or a silicon compound, and tin or a tin compound. Metal oxides such as TiO2 and SnO2 having a potential of less than 2V may also be used as the negative electrode active material. The carbon material may include low-crystalline carbon and / or highly crystalline carbon.

[0026] The separator 400 may include a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. The separator 400 may include a single porous polymer film or a laminate of a plurality of porous polymer films. As another embodiment of the present invention, the separator 400 may include a normal porous nonwoven fabric, for example, a high-melting glass fiber or a polyethylene terephthalate fiber.

[0027] The electrolyte 300 may include a salt having a structure such as A + B - . A + may include at least one or more alkali metal cations selected from the group consisting of Li + , Na + , and K + . B - may include 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 - may contain at least one anion selected from the group consisting of

[0028] As one embodiment of the present invention, the electrolyte 300 can be used by dissolving it in an organic solvent. The organic solvent may include 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, ethyl methyl carbonate (EMC), γ-butyrolactone, or a mixture thereof.

[0029] The casing of the secondary battery according to the embodiment of the present invention can adopt those commonly used in the relevant technical field, and there is no limitation on the outer shape according to the use of the battery. For example, the casing of the secondary battery may include a cylindrical shape, a rectangular shape, a pouch type, or a coin type.

[0030] FIG. 2 is a diagram showing a positive electrode active material according to an embodiment of the present invention. Referring to FIG. 2, the positive electrode active material CAM shows a powdery state before being used in the positive electrode active material layer AML1 described above with reference to FIG. 1. The positive electrode active material CAM may include a plurality of first particles PTC1, a plurality of second particles PTC2, and a plurality of aggregates ZAG.

[0031] The first particles PTC1 have a first average particle diameter APD1, and the second particles PTC2 may have a second average particle diameter APD2. The first average particle diameter APD1 may be smaller than the second average particle diameter APD2. For example, the first average particle diameter APD1 may be 1 μm to 5 μm. The second average particle diameter APD2 may be 10 μm to 25 μm. The "average particle diameter" used in the present invention, that is, D50, is the particle diameter when the volume cumulative percentage is 50% in the particle size distribution obtained from the volume of the particles. The average particle diameter can be measured by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or measured from an image of a transmission electron microscope or a scanning electron microscope. As another method, it can be measured using the dynamic light scattering method, data analysis is performed, the number of particles is counted for each particle size range, and then calculated to obtain the average particle diameter value. Unless otherwise defined, the average particle diameter may mean the diameter (D50) of the particles with a cumulative volume of 50% in the particle size distribution. Also, unless otherwise defined, the average particle diameter is obtained by measuring the sizes (diameter or major axis length) of randomly more than 20 particles in an image of a scanning electron microscope to obtain a particle size distribution, and taking the diameter (D50) of the particles with a cumulative volume of 50% in the said particle size distribution as the average diameter. In the present invention, the first particles PTC1 may be referred to as small particles, and the second particles PTC2 may be referred to as large particles.

[0032] The first and second particles PTC1, PTC2 may have a granular or spherical shape.

[0033] As one embodiment of the present invention, the first particle PTC1 may have a single-particle shape. As used herein, a single particle means a particle that exists independently without having a grain boundary within the particle and consists of one particle, and may refer to a single particle existing in an independent phase where particles are not mutually aggregated in a morphological phase, a monolith structure, or a single body structure, or non-aggregated particles, and may be, for example, a single crystal. Alternatively, the single particle may be a particle containing several crystals. The single particle may be in a form separated alone, or may exist in a form in which less than 10 single particles are attached to each other. The second particle PTC2 may have a secondary particle shape in which primary particles are aggregated.

[0034] The positive electrode active material CAM according to an embodiment of the present invention may be in a bimodal form including small grains (for example, PTC1) and large grains (for example, PTC2) having different average particle diameters. By filling the voids between the large grains with the small grains, the packing density of the positive electrode active material CAM can be improved. In other words, the positive electrode active material CAM according to an embodiment of the present invention may have a relatively high energy density per unit volume.

[0035] As one embodiment, the first particle PTC1 and the second particle PTC2 in the positive electrode active material CAM may have a weight ratio of 95:5 to 50:50. As another embodiment, the first particle PTC1 and the second particle PTC2 in the positive electrode active material CAM may have a weight ratio of 5:95 to 50:50. As an example, the weight of the second particle PTC2 in the positive electrode active material CAM may be greater than the weight of the first particle PTC1. Each of the first and second lithium composite oxides may contain nickel (Ni). Each of the first and second lithium composite oxides may further contain at least one or more metals selected from the group consisting of cobalt (Co), manganese (Mn), and aluminum (Al).

[0036] For example, the first lithium composite oxide may be represented by the following Chemical Formula 1. [Chemical Formula 1] Li a1 Nix1 Ma 1-x1 Zr w1 Y c1 O b1 In Chemical Formula 1, a1 ranges from 0.5 to 1.5, x1 ranges from 0.6 to 0.99, b1 ranges from 1.8 to 2.2, 1 - x1 ranges from 0.01 to 0.4, w1 ranges from 0.0005 to 0.003, and C1 can satisfy 0.00002 ≤ C1 ≤ 0.0003. Ma can contain at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. In one embodiment, Ma can contain Co, Al, and Mn.

[0037] The second lithium composite oxide can be represented by the following Chemical Formula 2. [Chemical Formula 2] Li a2 Ni x2 M b1-x2 O b2 In Chemical Formula 2, a2 ranges from 0.5 to 1.5, x2 ranges from 0.6 to 0.99, b2 ranges from 1.8 to 2.2, and 1 - x2 can range from 0.01 to 0.4. Mb can contain at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, Zr, and Sn. In one embodiment, Mb can contain Co, Al, and Mn. In the present invention, transition metals can also include post-transition metals such as Al.

[0038] For example, the second lithium composite oxide can be represented by the following Chemical Formula 2-1. [Chemical Formula 2-1] Li a2 Ni x2 Zr w2 Mb 1-x2-w2 O b2 In the formula (2-1), a2 can be from 0.5 to 1.5, x2 can be from 0.6 to 0.99, b2 can be from 1.8 to 2.2, w2 can be from 0.001 to 0.4, and 1 - x2 - w2 can be from 0.009 to 0.399. Mb can contain at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. In one embodiment, Mb can contain Co, Al, and Mn. In the present invention, transition metals can also be referred to as including post-transition metals such as Al.

[0039] The proportions of Mb and the elements constituting the second lithium composite oxide can be different from those of Ma and the elements constituting the first lithium composite oxide. For example, Mb of the second lithium composite oxide can contain Co and Al, and Ma of the first lithium composite oxide can contain Co and Mn. As another example, each of Ma and Mb can contain Co, Al, and Mn. At this time, the composition ratio of Al in Ma may be larger than the composition ratio of Al in Mb, and the composition ratio of Mn in Ma may be smaller than the composition ratio of Mn in Mb.

[0040] As shown in FIG. 2, the first particle PTC1 can contain doping particles on its surface. The doping particles can contain yttrium (Y) and zirconium (Zr). That is, the first particle PTC1 according to the present invention can contain yttrium (Y) and zirconium (Zr) on its surface. The yttrium (Y) and zirconium (Zr) contained on the surface can be derived from the "flux" described later. In one embodiment of the present invention, the flux can be yttria stabilized zirconia (YSZ).

[0041] The "composition of yttrium (Y)" or "composition of zirconium (Zr)" used in the present invention is obtained from the result of analyzing the elements on the surface of the cathode active material CAM using an energy dispersive spectrometer (EDX), that is, SEM-EDS. The atoms on the surface of the cathode active material CAM that collide with the electron beam can emit characteristic X-rays. The emitted X-rays are analyzed by an EDX detector, and the types and contents of the corresponding elements can be confirmed.

[0042] The "composition" used in the present invention may mean the content of elements constituting a specific compound. The "composition ratio" used in the present invention may mean the ratio of elements constituting a specific compound.

[0043] Yttrium (Y) on the surface of the first particle PTC1 may have a "first composition", and yttrium (Y) on the surface of the second particle PTC2 may have a "second composition".

[0044] According to the method for manufacturing a cathode active material described below, a small amount of yttrium (Y) may be detected on the surface of the second particle PTC2 by the step of mixing the first particle PTC1 and the second particle PTC2. According to the present invention, since the yttrium (Y) present on the surface of the second particle PTC2 may be contained in an extremely small amount by the mixing step, it may be regarded that yttrium (Y) is substantially omitted from the surface of the second particle PTC2.

[0045] In the present invention, the ratio of the first composition to the second composition may be greater than 100. Specifically, the ratio of the first composition to the second composition may be from 100 to 100,000. There may be no upper limit to the ratio of the first composition to the second composition. In the present invention, the composition of yttrium (Y) present on the surface of the small particles may be significantly more than the composition of yttrium (Y) present on the surface of the large particles.

[0046] The surface of the first particle PTC1 may have a composition ratio of Y to Zr (i.e., Y / Zr). The composition ratio (Y / Zr) may be from 0.5 to 20. As one embodiment, the doping particles on the surface of the first particle PTC1 may have the composition ratio (Y / Zr).

[0047] If the composition ratio (Y / Zr) is within the above-described range, the ionic conductivity of the lithium secondary battery can be effectively improved.

[0048] As one embodiment of the present invention, x1, which is the molar ratio of Ni in Chemical Formula 1, may be greater than 0.8. If the first lithium composite oxide has a high nickel content composition (x1>0.8), the firing of the first lithium composite oxide can be carried out at a relatively low temperature. Thereby, in the manufacturing process of the positive electrode active material for a lithium secondary battery described later, the first particle PTC1 can be synthesized at a relatively low temperature. Ni in the first lithium composite oxide can affect the output and capacity of the lithium secondary battery. The present invention can provide a high-output lithium secondary battery by using a first lithium composite oxide having a high nickel content composition. x2, which is the molar ratio of Ni in Chemical Formula 2, may also be greater than 0.8. However, x2 may be different from x1.

[0049] As the content of Ni in the first and second lithium composite oxides increases, the stability of the positive electrode or the secondary battery may decrease. As one embodiment of the present invention, the first and second lithium composite oxides may further contain Co, thereby improving the stability and capacity retention characteristics of the secondary battery.

[0050] According to one embodiment of the present invention, the first particle PTC1 may have a single-particle shape. The first particle PTC1 may be more durable and denser than the second particle PTC2. Therefore, the formation of fine cracks inside the first particle PTC1 can be prevented. As a result, the stability and capacity retention characteristics of the secondary battery according to the present invention can be improved.

[0051] In order for the first particle PTC1 having a single-particle shape to form the first lithium composite oxide, a firing process can be performed at a temperature lower than 1000°C. However, in such a case, the residual lithium on the surface of the first particle PTC1 may increase, and the ionic conductivity on the surface of the first particle PTC1 may decrease. As a result, the output characteristics and capacity characteristics of the secondary battery may decrease somewhat.

[0052] As described above, the second particle PTC2 may have a secondary particle shape. In this case, fine cracks (micro-cracks) may be formed inside the secondary particles during charge and discharge of the battery, promoting a side reaction between the electrolyte (see 300 in FIG. 1) and the positive electrode active material CAM, and gas may be generated inside the battery. As a result, the stability and life of the secondary battery may decrease.

[0053] According to an embodiment of the present invention, the first particle PTC1 may contain yttrium (Y) on its surface. In the present invention, the yttrium (Y) is doped at the position of the transition metal of the positive electrode active material, and the yttrium (Y) serves as a pillar, so that Li + and Ni 2+ The cation mixing phenomenon occurring between them can be suppressed to improve the life of the secondary battery.

[0054] In addition, by doping yttrium (Y) having a large ionic radius on the surface of the first particle PTC1, the resistance inside the electrode can be reduced to improve the output characteristics of the secondary battery.

[0055] Also, according to an embodiment of the present invention, the first particle PTC1 may contain zirconium (Zr) on its surface. Thereby, the ionic conductivity of the surface of the first particle PTC1 can be increased. In other words, even if the first particle PTC1 is fired at a relatively low temperature and has a single-particle shape, the durability and capacity maintenance characteristics of the secondary battery can be improved by the surface containing Zr. That is, since the first particle PTC1 contains Zr on its surface, side reactions between the first particle PTC1 and the electrolyte 300 can be prevented by the surface. In other words, the present invention can prevent the deterioration of the first particle PTC by the electrolyte 300. Further, the first particle PTC1 according to the present invention may have a relatively large grain size due to Zr. Thereby, the first particle PTC1 has high durability and can prevent fine cracks inside the particle.

[0056] The aggregate ZAG may be provided in the space between the first and second particles PTC1 and PTC2. The aggregate ZAG may be derived from a flux described later. The aggregate ZAG may contain at least one of cobalt (Co), aluminum (Al), and zirconium (Zr). For example, the aggregate ZAG may be a mass formed by aggregating a part of the flux that is not coated on the surfaces of the first and second particles PTC1 and PTC2. The aggregate ZAG is shown in FIG. 2, but in the present invention, the aggregate ZAG does not necessarily have to be present.

[0057] FIG. 3 is a sequence diagram showing a method for manufacturing a positive electrode active material according to an embodiment of the present invention. FIGS. 4 to 6 are schematic diagrams showing the method for manufacturing the positive electrode active material of FIG. 3.

[0058] Referring to FIGS. 3 and 4, the first particle PTC1 can be synthesized (S100).

[0059] A method for synthesizing the first particle PTC1 will be described in detail. First, the first precursor PRE1 can be prepared. The first precursor PRE1 may contain Ni and Ma of Chemical Formula 1 described above. Ma may contain at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. For example, Ma may contain Co and Mn.

[0060] As one embodiment, the first precursor PRE1 may be obtained by a coprecipitation method. For example, the coprecipitation method may include dissolving a raw material substance of a transition metal in a solvent such as distilled water, and continuously introducing a transition metal salt solution into a reactor together with a chelating agent and a basic aqueous solution to cause precipitation. After collecting the precipitate in a slurry state, the slurry solution may be filtered and dried to obtain the first precursor PRE1 which is a metal composite oxide.

[0061] In the present invention, the raw material substance of the transition metal may contain a metal salt of at least one element selected from the group consisting of Ni, Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. The metal salt may be a sulfate, nitrate, acetate, halide, hydroxide, etc., and is not particularly limited as long as it can be dissolved in a solvent. The raw material substance of the transition metal according to this embodiment may contain a nickel salt, a cobalt salt, and an aluminum salt. The raw material substance of the transition metal can be mixed by adjusting the molar ratio so that the positive electrode active material has high capacity characteristics. For example, x1 of Chemical Formula 1 can be determined by the molar ratio.

[0062] The first precursor PRE1, a lithium raw material, and a flux can be mixed in a certain ratio to form a mixture. For example, the first precursor PRE1, a lithium raw material, and a flux can be mixed at a molar ratio of about 1.06:1:0.02. The lithium raw material is not particularly limited as long as it is a substance usually used in manufacturing a positive electrode active material. For example, the lithium raw material may include a lithium salt such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate.

[0063] If the melting agent is introduced and mixed, the melting agent and the lithium raw material may react to form an intermediate in a liquid state. In this case, a rearrangement phenomenon may occur to reduce the surface tension while the intermediate reacts with the first precursor PRE1. After the rearrangement, a solution reprecipitation phenomenon may occur, and the pores inside the particles of the lithium-transition metal composite oxide may decrease. For example, the reprecipitated particles of the lithium-transition metal composite oxide may have a single-particle shape through densification. That is, single particles can be smoothly formed by the melting agent, and a doping substance can be formed on the surface of the single particles.

[0064] The melting agent may contain yttrium (Y) and zirconium (Zr). Preferably, the melting agent is Zr (1-x) Y x O 2-x / 2 (0.01 ≦ x ≦ 0.30). The composition ratio (Y / Zr) of the yttrium (Y) to the zirconium (Zr) in the melting agent may be 0.5 to 20.

[0065] That is, the present invention can dope Zr and Y on the surface of the first particles PTC1 in the firing process described below by using the melting agent. As an embodiment of the present invention, YSZ can be used as the melting agent. The present invention can obtain a single crystallization process by introducing YSZ during firing, and the introduced YSZ acts as a grain growth promoter. That is, the present invention may have an effect of improving productivity due to a decrease in the firing temperature because YSZ serves as an aggregation inhibitor.

[0066] Next, the mixture can be introduced into furnace FRC and the first firing step STR1 can be performed at the first temperature. The first temperature can be from 600°C to 1,000°C. More specifically, the first temperature can be from 650°C to 900°C. The first firing step STR1 can be performed in an oxidizing atmosphere such as air or oxygen. The heat treatment time of the first firing step STR1 can be from 10 hours to 30 hours. As another embodiment of the present invention, a preliminary firing may be additionally performed at 150°C to 800°C before the first firing step STR1.

[0067] The first particles PTC1 can be formed from a mixture containing the first precursor PRE1, a lithium raw material, and a flux by the first firing step STR1. As another embodiment of the present invention, a grinding step can be performed on the synthesized first particles PTC1. The ground first particles PTC1 can have the first average particle diameter APD1 described with reference to FIG. 2. The average particle diameter of the first particles can be from 1 μm to 5 μm.

[0068] Referring to FIGS. 3 and 5, the second particles PTC2 can be synthesized (S200). A method for synthesizing the second particles PTC2 will be described in detail. As one embodiment, the second precursor PRE2 may be obtained in substantially the same or similar manner as the first precursor PRE1. However, the average particle diameter of the second precursor PRE2 can be manufactured to be larger than the average particle diameter of the first precursor PRE1.

[0069] First, the second precursor PRE2 can be prepared. The second precursor PRE2 can contain Ni and Mb of Chemical Formula 2 described above. Mb can contain at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, Zr, and Sn. For example, Mb can contain Co and Mn.

[0070] As an embodiment, the second precursor PRE2 may be obtained by a coprecipitation method. For example, the coprecipitation method may include dissolving a raw material substance of a transition metal in a solvent such as distilled water, and continuously introducing a transition metal salt solution into a reactor together with a chelating agent and a basic aqueous solution to cause precipitation. After collecting the precipitate in a slurry state, the slurry solution may be filtered and dried to obtain the second precursor PRE2 which is a metal composite oxide.

[0071] In the present invention, the raw material substance of the transition metal may include a metal salt of at least one element selected from the group consisting of Ni, Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. As the metal salt, sulfates, nitrates, acetates, halides, hydroxides, etc. may be used, and there is no particular limitation as long as it can be dissolved in a solvent. The raw material substance of the transition metal according to this embodiment may include a nickel salt, a cobalt salt, and an aluminum salt. The raw material substances of the transition metal may be mixed by adjusting the molar ratio so that the positive electrode active material has high capacity characteristics. For example, x2 in Chemical Formula 2 may be determined by the molar ratio.

[0072] The second precursor PRE2 may be mixed with a lithium raw material in a certain ratio to form a mixture. For example, the second precursor PRE2 and the lithium raw material may be mixed at a molar ratio of about 1:1. The lithium raw material is not particularly limited as long as it is a substance usually used in manufacturing the positive electrode active material. For example, the lithium raw material may include a lithium salt such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate.

[0073] The mixture may be introduced into the furnace FRC and the second firing step STR2 may be performed at a second temperature. The second temperature may be 700°C to 1,000°C. More specifically, the second temperature may be 700°C to 800°C. As an example, the second temperature may be lower than the first temperature. The heat treatment time of the second firing step STR2 may be 10 hours to 30 hours.

[0074] The second particles PTC2 can be formed from a mixture containing the second precursor PRE2 and a lithium raw material by the second firing step STR2. As another embodiment of the present invention, a grinding step can be performed on the synthesized second particles PTC2. The ground second particles PTC2 can have the second average particle diameter APD2 described with reference to FIG. 2. The average particle diameter of the second particles PTC2 can be from 10 μm to 25 μm.

[0075] Other descriptions regarding the second firing step STR2 can be the same as or similar to the first firing step STR1.

[0076] Referring to FIGS. 3 and 6, the first particles PTC1 and the second particles PTC2 can be synthesized with each other (S300). As one embodiment, the first particles PTC1 and the second particles PTC2 can be mixed at a weight ratio of 95:5 to 50:50. As another embodiment, the first particles PTC1 and the second particles PTC2 may be mixed at a weight ratio of 5:95 to 50:50. By mixing the first particles PTC1 and the second particles PTC2 having different average particle diameters from each other, a positive electrode active material in a bimodal form can be prepared. The mixed first and second particles PTC1, PTC2 can be washed and dried.

[0077] Additionally, a coating step can be further performed on the first and second particles PTC1, PTC2. The coating step can include coating at least one of cobalt and aluminum on the surfaces of the first and second particles PTC1, PTC2.

[0078] Specifically, the first and second particles PTC1, PTC2 and the coating raw material substance CTS can be mixed. The coating raw material substance CTS can be a cobalt compound, an aluminum compound, or a mixture thereof. For example, the cobalt compound can include cobalt sulfate, but is not particularly limited thereto.

[0079] The first and second particles PTC1, PTC2 and the coating raw material substance CTS can be put into a solvent (for example, distilled water) and mixed. The first and second particles PTC1, PTC2 and the coating raw material substance CTS can be uniformly mixed by a stirrer MXU. Next, after the first and second particles PTC1, PTC2 are filtered and dried, a surface treatment can be performed on the first and second particles PTC1, PTC2. The surface treatment may include performing a heat treatment process in an oxidizing atmosphere such as air or oxygen. The surface treatment can be performed at a temperature of 500°C to 800°C.

[0080] As another embodiment of the present invention, the coating process may include a dry coating process. For example, a mixture of the first and second particles PTC1, PTC2 and a coating raw material substance (for example, cobalt hydroxide) can be put into a dry coater without a solvent and stirred and mixed. The surface treatment can be performed on the obtained dry mixture.

[0081] In the heat treatment process, a mixture of the first and second particles PTC1, PTC2 and the coating raw material substance CTS can be put into a furnace FRC, and a third firing process can be performed at a third temperature. The third temperature can be 700°C to 1,000°C. More specifically, the third temperature can be 650°C to 900°C, preferably 650°C to 750°C.

[0082] Thereby, the positive electrode active material CAM according to the embodiment of the present invention described with reference to FIG. 2 can be manufactured.

[0083] The positive electrode 100 in FIG. 1 can be manufactured by a normal positive electrode manufacturing method except that the positive electrode active material CAM according to the embodiment of the present invention is used. Specifically, the positive electrode active material CAM, binder, and conductive material of the present invention can be dissolved or dispersed in a solvent to produce a mixture. The binder and the conductive material can be the same as those described above for the positive electrode active material layer AM1 in FIG. 1. After the mixture is applied onto the first current collector COL1, the positive electrode 100 can be manufactured by drying and rolling.

[0084] The solvent can be a solvent generally used in the relevant technical field. For example, it may include at least one of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, and combinations thereof.

[0085] In another embodiment, the mixture can be cast onto a separate support to produce a film, that is, the positive electrode active material layer AML1. The positive electrode 100 can be manufactured by laminating the positive electrode active material layer AML1 on the first current collector COL1.

[0086] FIG. 7 is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 7, the lithium secondary battery may include a positive electrode 100, a negative electrode 200, and a separator 400. The descriptions of the positive electrode 100, negative electrode 200, and separator 400 in FIG. 7 may be substantially the same as those described for the lithium secondary battery in FIG. 1 above.

[0087] The positive electrode 100, negative electrode 200, and separator 400 in FIG. 7 may be wound or folded to form an electrode assembly. The electrode assembly can be housed in the battery casing 500. The electrode assembly may include a plurality of electrode assemblies. A separator 400 may be provided between the electrode assemblies. The electrode assemblies stacked sequentially may be provided in the battery casing 500. The inside of the battery casing 500 may be filled with an electrolyte (see 300 in FIG. 1). The battery casing 500 can be sealed by a cap assembly 600. The battery casing 500 according to an embodiment of the present invention can be cylindrical, rectangular, or pouch-shaped. The lithium secondary battery according to an embodiment of the present invention can be used in devices such as laptop computers, smartphones, or electric vehicles.

[0088] Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

[0089] Example 1: Production of Cathode Active Material Production Example 1: Production of Small Particle Precursors A small-particle precursor was produced using the coprecipitation method. Through the process described below, nickel-based metal hydroxide (Ni 0.94 Co 0.05 Mn 0.01 (OH)2) was produced.

[0090] As raw materials for the nickel-based metal hydroxide, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent so as to have a molar ratio of 90:7:3 to prepare a metal raw material mixture solution. The metal raw material mixture solution, aqueous ammonia, and sodium hydroxide were put into a reactor and reacted.

[0091] The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed substance was dried in a hot air oven at 210 °C for 24 hours to obtain a small-particle precursor (Ni 0.90 Co 0.07 Mn 0.03 (OH)2) powder with a particle size of about 3 μm.

[0092] Production Example 2: Production of Small-Particle Lithium Composite Oxide The small-particle precursor of Production Example 1, anhydrous lithium hydroxide (LiOH), and a melting agent (YSZ) were dry-mixed using a Henschel mixer. Lithium, transition metal, and the melting agent were mixed at a molar ratio of about 1.06:1:0.02. The transition metal is the total of the transition metals contained in the small-particle precursor (Ni + Co + Mn). The melting agent has a composition ratio of Y to Zr (Y / Zr) of about 8.695.

[0093] The mixture was heat-treated (i.e., the first firing step) at about 800 °C for 15 hours in an oxygen atmosphere to synthesize first particles which are the first lithium composite oxide. The first particles were ground with a jet mill at a pressure of 3 bar.

[0094] Production Example 3: Production of Large-Particle Precursor A large-particle precursor was produced using the coprecipitation method. Through the process described below, nickel-based metal hydroxide (Ni0.94 Co 0.05 Al 0.01 (OH)2) was produced.

[0095] As raw material substances for nickel-based metal hydroxides, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3·H2O) were dissolved in distilled water as a solvent so as to have a molar ratio of 90:7:3 to prepare a metal raw material mixture solution. To form a complex compound, a diluted solution of aqueous ammonia (NH4OH) and sodium hydroxide (NaOH) as a precipitate were prepared. Next, the metal raw material mixture solution, aqueous ammonia, and sodium hydroxide were charged into a reactor. Lithium hydroxide was charged to maintain the pH of the mixture in the reactor. The reaction was carried out for about 20 hours while stirring the mixture in the reactor.

[0096] The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed substance was dried in a hot air oven at 190 °C for 24 hours to obtain a large particle precursor (Ni 0.90 Co 0.07 Al 0.03 (OH)2) powder.

[0097] Production Example 4: Production of large particle lithium composite oxide The large particle precursor of Production Example 3 and anhydrous lithium hydroxide (LiOH) were mixed dry using a Henschel mixer. Lithium and transition metals were mixed at a molar ratio of about 1:1. The transition metal is the total of the transition metals contained in the large particle precursor (Ni + Co + Al). The mixture was heat-treated (i.e., the second firing step) at about 750 °C for 15 hours in an oxygen atmosphere to synthesize second particles which are a second lithium composite oxide. The second particles were pulverized with a jet mill at a pressure of 3 bar.

[0098] Production Example 5: Production of bimodal particles The second particles (Production Example 4) with an average particle size of 18 μm and the first particles (Production Example 2) with an average particle size of 3 μm were mixed at a weight ratio of 70:30 to prepare bimodal particles. The bimodal particles were put into distilled water and washed. 2 mol% of cobalt sulfate was put into sodium hydroxide to perform wet cobalt coating.

[0099] After performing the filtration and drying steps, a mixture of 5 mol% of sodium hydroxide and 0.005 mol% of zirconium oxide (ZrO₂) was heat-treated (i.e., surface-treated) at about 700 °C for 15 hours in an oxygen atmosphere to complete the cobalt coating. Thus, the cathode active material according to this example was obtained.

[0100] Production Example 6: Production of Lithium Secondary Battery 96 g of the cathode active material of Production Example 5, 2 g of polyvinylidene fluoride, 47 g of the solvent N-methylpyrrolidone, and 2 g of the conductive agent carbon black were mixed to produce an active material slurry.

[0101] The active material slurry was coated on an aluminum foil using a doctor blade to produce a thin plate-like electrode. After drying the electrode at 135 °C for 3 hours or more, a cathode was produced through a rolling and vacuum drying process.

[0102] As a counter electrode to the cathode, a 2032-type coin cell was produced using a lithium metal counter electrode. A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was interposed between the cathode and the lithium metal counter electrode. An electrolyte was injected to fabricate a 2032-type coin cell. As the electrolyte, a solution in which 1.1 M of LiPF₆ was dissolved in a solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3:5 was used.

[0103] Comparative Example 1 A lithium secondary battery was produced in the same manner as in Example 1, except that a melting agent (YSZ) was added and mixed in Production Example 4 and zirconium oxide (ZrO₂) was not added in Production Example 5.

[0104] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the melting agent (YSZ) was not used in Production Example 2.

[0105] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the melting agent (YSZ) was not used in Production Example 2 and zirconium oxide (ZrO2) was not added in Production Example 5.

[0106] Experimental Example 1: Analysis of Elements of Cathode Active Material (SEM-EDS) The positive electrode active material produced in Example 1 was photographed with a scanning transmission electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) was performed. Thereby, the elements on the surface of the first particles (small particles) and the elements on the surface of the second particles (large particles) were analyzed.

[0107] The SEM photograph of the surface of the first particle PTC1 of the positive electrode active material produced in Example 1 is shown in FIG. 8A. And the EDS result which measured the component of the 1st particle PTC1 is shown in FIG. 8B.

[0108] The SEM photograph of the surface of the second particle PTC2 of the positive electrode active material produced in Example 1 is shown in FIG. 9A. And the EDS result which measured the component of the 2nd particle PTC2 is shown in FIG. 9B.

[0109] Referring to FIGS. 8A and 8B, it was confirmed that zirconium (Zr) and yttrium (Y) were doped uniformly on the surface of the first particle PTC1 which is a small particle.

[0110] The "surface" used in the present invention may mean the outermost layer of the particle. Referring to FIGS. 8A and 8B, it was confirmed that zirconium (Zr) and yttrium (Y) were doped uniformly in the outermost layer of the first particle PTC1.

[0111] Referring to FIGS. 9A and 9B, it was confirmed that there was almost no composition of Y in the second large particle PTC2.

[0112] That is, it was confirmed that yttrium (Y) was uniformly doped on the surface of the small particles according to the examples, and only a very small amount of yttrium (Y) was doped on the surface of the large particles.

[0113] Experimental Example 2: Life Characteristics of Lithium Secondary Battery The capacity retention rates of the coin cells of Example 1 and Comparative Examples 1 to 3 were evaluated as follows using a charger (manufacturer: TOYO, model: TOYO-3100).

[0114] Each coin cell was subjected to constant current charging at 45° C. with a current of 1C until it reached 4.3V, and then constant voltage charging was carried out until it reached a current of 0.05C. After the charging of the cell was completed, after a rest period of about 10 minutes, a cycle of constant current discharging at a current of 1C until the voltage reached 3V was repeated 150 times for evaluation.

[0115] Table 1 shows the capacity and retention rate characteristics of the coin cells of the examples and the comparative examples. In Table 1 below, the "high-temperature life value" is a value obtained by measuring the discharge capacity at 50 times after repeating charge and discharge 50 times at 1C at 45° C. after the first charge and discharge, and calculating the ratio (%) of the discharge capacity at 50 times to the first discharge capacity. That is, the "high-temperature life value" means the capacity retention rate.

[0116]

Table 1

[0117] Referring to Table 1, it was confirmed that the capacity retention rate characteristics of the coin cells of the examples were improved compared to those of the comparative examples. It was confirmed that the composition of yttrium (Y) present on the surface of the small particles was doped in a stepwise manner compared to the composition of yttrium (Y) present on the surface of the large particles, and the capacity retention rate characteristics of the lithium secondary battery were improved.

[0118] That is, in order to overcome the difference in electrical conductivity between large grains of polycrystals and small grains of single crystals, in order to increase the electrical conductivity of the small grains of single crystals, a flux such as YSZ is applied only to the small grains to bring out the balance of electrical conductivity between the large grains and the small grains, thereby improving the capacity retention rate of the lithium secondary battery.

[0119] As described above, specific examples of the present invention have been described with reference to the drawings and examples. However, the present invention may be implemented in other specific forms without changing its technical idea and essential features. Therefore, it should be understood that the above-described examples are illustrative in all respects and not restrictive.

Claims

1. first particles including a first lithium composite oxide and having a first average particle size; second particles including a second lithium composite oxide and having a second average particle size larger than the first average particle size; Including, the first particles include yttrium (Y) and zirconium (Zr) on a surface thereof; the yttrium (Y) on the surface of the first particle has a first composition; the yttrium (Y) on the surface of the second particles has a second composition; the ratio of the first composition to the second composition being greater than 100;

2. The positive electrode active material according to claim 1 , wherein the first lithium composite oxide is represented by the following Chemical Formula 1: [Chemical formula 1] Li a1 Ni x1 Ma 1-x1 Zr w1 Y c1 O b1 In Formula 1, a1 is 0.5 to 1.5, x1 is 0.6 to 0.99, b1 is 1.8 to 2.2, 1-x1 is 0.01 to 0.4, w1 is 0.0005 to 0.003, C1 is 0.00002≦C1≦0.0003, and Ma includes at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn.

3. The positive electrode active material of claim 1 , wherein the first particles have a composition ratio (Y / Zr) of the yttrium (Y) to the zirconium (Zr) of 0.5 to 20.

4. the first particles are single crystals; The positive electrode active material according to claim 1 .

5. The first particles have an average particle size of 1 μm to 5 μm. The positive electrode active material according to claim 1 .

6. The positive electrode active material according to claim 1 , wherein the second lithium composite oxide is represented by the following formula 2: [Chemical 2] Li a2 Ni x2 Ma 1-x2 O b2 In Formula 2, a2 ​​is 0.5 to 1.5, x2 is 0.6 to 0.99, b2 is 1.8 to 2.2, 1-x2 is 0.01 to 0.4, and Mb includes at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, Zr, and Sn.

7. The positive electrode active material according to claim 1 , wherein the second particles have surfaces that are substantially free of yttrium (Y).

8. The positive electrode active material of claim 1 , wherein the second particles are secondary particles including a plurality of primary particles.

9. The cathode active material of claim 1 , wherein the second particles are polycrystalline.

10. The second particles have an average particle size of 10 μm to 25 μm. The positive electrode active material according to claim 1 .

11. The positive electrode active material of claim 1 , wherein the second particles and the first particles have a weight ratio of 95:5 to 50:

50.

12. synthesizing first particles comprising a first lithium composite oxide and having a first average particle size; synthesizing second particles comprising a second lithium composite oxide and having a second average particle size larger than the first average particle size; mixing the first particles and the second particles; Including, Synthesizing the first particles comprises: providing a precursor of the first particles; calcining the precursor with a flux; The method for producing a positive electrode active material, wherein the flux contains yttrium (Y) and zirconium (Zr).

13. The method for producing a positive electrode active material according to claim 12, wherein the composition ratio (Y / Zr) of the yttrium (Y) to the zirconium (Zr) in the flux is 0.5 to 20.

14. The method of claim 12 , wherein the synthesis of the first particles is performed at 650° C. to 900° C. for 10 to 30 hours.

15. The first particles have an average particle size of 1 μm to 5 μm; The method of claim 12, wherein the second particles have an average particle size of 10 to 25 μm.

16. The method for producing a positive electrode active material according to claim 12 , wherein the first lithium composite oxide is represented by the following Chemical Formula 1: [Chemical formula 1] Li a1 Ni x1 Ma 1-x1 Zr w1 Y c1 O b1 In Formula 1, a1 is 0.5 to 1.5, x1 is 0.6 to 0.99, b1 is 1.8 to 2.2, 1-x1 is 0.01 to 0.4, w1 is 0.0005 to 0.003, C1 is 0.00002≦C1≦0.0003, and Ma includes at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn.

17. The method for producing a positive electrode active material according to claim 12 , wherein the second lithium composite oxide is represented by the following Chemical Formula 2: [Chemical 2] Li a2 Ni x2 Ma 1-x2 O b2 In Formula 2, a2 ​​is 0.5 to 1.5, x2 is 0.6 to 0.99, b2 is 1.8 to 2.2, 1-x2 is 0.01 to 0.4, and Mb includes at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, Zr, and Sn.

18. The method of claim 12, wherein the mixing of the first particles and the second particles comprises mixing the second particles and the first particles in a weight ratio of 95:5 to 50:

50.

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

20. A lithium secondary battery comprising the positive electrode according to claim 19.

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