Mixed cathode material and preparation method therefor

Abstract

The present invention relates to a mixed cathode material and a preparation method therefor, the material comprising a first cathode active material, which includes a first lithium transition metal oxide, and a second cathode active material, which includes a second lithium transition metal oxide, wherein each of the first lithium transition metal oxide and the second lithium transition metal oxide has a nickel content of 70 mol% or more on the basis of the total metal excluding lithium, D50 of the first cathode active material is greater than D50 of the second cathode active material, and the results of EELS analysis on the particle surfaces of each of the first cathode active material and the second cathode active material satisfy relation 1.

Description

Mixed cathode material and method for producing the same This application claims the benefit of priority to Korean Patent Application No. 10-2023-0123472, filed September 15, 2023, and Korean Patent Application No. 10-2024-0123370, filed September 10, 2024, the entire contents of which are incorporated herein by reference. The present invention relates to a mixed cathode material and a method for producing the same, a cathode comprising the mixed cathode material, and a lithium secondary battery comprising the cathode. The recent rapid proliferation of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity secondary batteries. In particular, lithium secondary batteries, with their lightweight design and high energy density, are attracting attention as power sources for portable devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries. Lithium secondary batteries produce electrical energy through oxidation and reduction reactions when lithium ions are inserted / deintercalated between the positive and negative electrodes, which are made of active materials capable of intercalating and deintercalating lithium ions, while charging an organic electrolyte or polymer electrolyte between them. Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), lithium iron phosphate compound (LiFePO4), etc. have been used as positive active materials for lithium secondary batteries. In addition, as a method to improve the low thermal stability of LiNiO2 while maintaining the excellent reversible capacity, lithium composite metal oxides (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxides') in which some of the nickel (Ni) is replaced with cobalt (Co) and manganese (Mn) have been developed. However, the conventionally developed NCM-based lithium composite transition metal oxides have insufficient capacity characteristics, which limits their application. To address these issues, recent research has focused on increasing the nickel content in NCM lithium composite transition metal oxides. However, high-nickel (High-Ni) cathode active materials with high nickel content suffer from the following problems: Due to the high reactivity of nickel, they generate large amounts of gas during charge / discharge processes, exhibit significant lattice structural instability due to cation mixing and oxygen desorption, and increase the content of lithium impurities remaining on the surface. High-nickel cathode active materials typically undergo a washing process during manufacturing, as increased lithium impurity content can lead to gelation and swelling in the cathode slurry. While this washing process removes surface lithium byproducts, reducing gas production, it can also cause surface damage to the cathode active material particles, potentially negatively impacting battery life and storage. The present invention is intended to solve the above problems, and provides a method for effectively removing lithium byproducts remaining on the surface without damaging the particle structure when manufacturing a cathode material having a high nickel content and a bimodal form, and a cathode material manufactured using the method and exhibiting excellent resistance and life characteristics. [1] The present invention comprises a first positive electrode active material comprising a first lithium transition metal oxide and a second positive electrode active material comprising a second lithium transition metal oxide, wherein the first lithium transition metal oxide and the second lithium transition metal oxide each have a nickel content of 70 mol% or more among the total metals excluding lithium, and D of the first positive electrode active material 50 D of the above second positive electrode active material 50 A mixed cathode material is provided, wherein the EELS analysis results for the particle surfaces of the first cathode active material and the second cathode active material satisfy the following equation 1. [Formula 1] I(854eV) / I(855.5eV) < 1 In the above equation 1, I(854 eV) is the peak intensity that appears around 854 eV, I(855.5 eV) is the peak intensity that appears around 855.5 eV. [2] The present invention provides a mixed cathode material in the above [1], wherein the I(854 eV) / I(855.5 eV) value of the above formula 1 is 0.85 or more. [3] The present invention provides a mixed cathode material in which, in the above [1] or [2], the molar ratio of lithium to all metal elements excluding lithium in the first lithium transition metal oxide is 1.01 to 1.09. [4] The present invention provides a mixed cathode material, wherein, in at least one of the above [1] to [3], the molar ratio of lithium to all metal elements excluding lithium in the second lithium transition metal oxide is 1.01 to 1.04. [5] The present invention provides a mixed cathode material in which the weight ratio of the first cathode active material and the second cathode active material is 6:4 to 8:2 in at least one of the above [1] to [4]. [6] The present invention provides a mixed cathode material, wherein in at least one of the above [1] to [5], the first lithium transition metal oxide is represented by the following chemical formula 1. [Chemical Formula 1] Li a Ni b Co c Mn d Q e O 2+f In the above chemical formula 1, a, b, c, d, e and f are 1.01≤a≤1.09, 0.7≤b<1.0, 0 respectively <c<0.3, 0<d<0.3, 0≤e≤0.1, b+c+d+e=1, -0.1≤f≤1.0이고, Q is at least one selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. [7] The present invention provides a mixed cathode material, wherein in at least one of the above [1] to [6], the second lithium transition metal oxide is represented by the following chemical formula 2. [Chemical Formula 2] Li g Ni h Co i Mn j Q' k O 2+q In the above chemical formula 2, g, h, i, j, k and q are 1.01≤g≤1.04, 0.7≤h<1.0, 0, respectively. <i<0.3, 0<j<0.3, 0≤k≤0.1, h+i+j+k=1, -0.1≤q≤1.0이고, Q' is at least one selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. [8] The present invention, in at least one of the above [1] to [7], D of the first positive electrode active material 50 A mixed cathode material having a diameter of 8㎛ to 15㎛ is provided. [9] The present invention, in at least one of the above [1] to [8], D of the second positive electrode active material 50 A mixed cathode material having a diameter of 2㎛ to 5㎛ is provided.

[0010] The present invention comprises the steps of: mixing and firing a first precursor containing nickel of 70 mol% or more based on the total moles of transition metals and a first lithium source to produce a first sintered body; washing the first sintered body with 50 to 70 parts by weight of a washing solution based on 100 parts by weight of the first sintered body to produce a first lithium transition metal oxide; mixing and firing a second precursor containing nickel of 70 mol% or more based on the total moles of transition metals and a second lithium source to produce a second sintered body; and washing the second sintered body with 60 to 80 parts by weight of a washing solution based on 100 parts by weight of the second sintered body to produce a second lithium transition metal oxide, wherein D of the first lithium transition metal oxide 50 D of the above second lithium transition metal oxide 50 A method for producing a mixed cathode material according to at least one of [1] to [9] is provided.

[0011] The present invention provides a method for producing a mixed cathode material, wherein, in the step of producing the first sintered body in the above

[0010] , the first precursor and the first lithium source are mixed so that the molar ratio of lithium in the first lithium source to the total metal elements of the first precursor (Li / M)1 is 1.03 to 1.09.

[0012] The present invention provides a method for producing a mixed cathode material, wherein in the step of producing the second sintered body in the above

[0010] or

[0011] , the second precursor and the second lithium source are mixed so that the molar ratio of lithium in the second lithium source to the total metal elements of the second precursor (Li / M)2 is 1.01 to 1.04.

[0013] The present invention provides a method for producing a mixed cathode material, further comprising a step of mixing the first lithium transition metal oxide and the second lithium transition metal oxide in a weight ratio of 6:4 to 8:2 in at least one of the above

[0010] to

[0012] .

[0014] The present invention provides a method for producing a mixed cathode material, wherein, in at least one of the above

[0010] to

[0013] , the washing step of producing the first lithium transition metal oxide is performed by placing the first sintered body in water and stirring it at a temperature of 15°C to 25°C at a speed of 1,500 rpm to 2,500 rpm for 1 to 20 minutes.

[0015] The present invention provides a method for producing a mixed cathode material, wherein, in at least one of the above

[0010] to

[0014] , the washing step of producing the second lithium transition metal oxide is performed by putting the second sintered body in water and stirring it at a temperature of 15°C to 25°C at a speed of 1,500 rpm to 2,500 rpm for 1 to 20 minutes.

[0016] The present invention provides a method for producing a mixed cathode material, wherein, in at least one of the above

[0010] to

[0015] , the firing in the step of producing the first sintered body is performed at 700°C to 900°C.

[0017] The present invention provides a method for producing a mixed cathode material, wherein, in at least one of the above

[0010] to

[0016] , the firing in the step of producing the second sintered body is performed at 700°C to 900°C.

[0018] The present invention provides a positive electrode comprising at least one mixed positive electrode material among the above [1] to [9].

[0019] The present invention provides a lithium secondary battery comprising the positive electrode of the above

[0018] ; a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and an electrolyte. The present invention provides a mixed cathode material capable of realizing high energy density by including a high nickel content and having a high capacity and a bimodal form, and a method for manufacturing the same. In addition, in manufacturing a high-nickel cathode active material for which a washing process is essential, separate optimal washing conditions are provided for small particles with relatively large surface areas and large particles with relatively small surface areas, so that lithium byproducts remaining on the surface can be effectively removed without damaging the particles. In addition, by applying different ratios of the number of lithium moles to the total number of metal moles excluding lithium in the highly reactive small particles due to their large surface areas and in the non-reactive large particles (hereinafter referred to as the Li / M mole ratio), the problem of excessive formation of lithium byproducts after calcination in the small particles and the deterioration of structural stability in the large particles can be prevented. Ultimately, it is possible to provide a blended cathode material with excellent resistance and life characteristics. FIG. 1 is a diagram showing EELS spectra for the surface of the first positive electrode active material manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention. FIG. 2 is a diagram showing EELS spectra for the surface of the second positive electrode active material manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention. FIG. 3 is a diagram showing an EELS spectrum for the surface of the first positive electrode active material manufactured in Comparative Examples 3 and 4 of the present invention. FIG. 4 is a diagram showing the EELS spectrum for the surface of the second positive electrode active material manufactured in Comparative Examples 3 and 4 of the present invention. Hereinafter, the present invention will be described in more detail to help understand the present invention. In the present invention, “EELS analysis result” means an EELS spectrum obtained by electron energy loss spectroscopy (EELS). The EELS spectrum can be obtained using HR-TEM equipment, and the horizontal axis represents the loss energy region and the vertical axis represents the peak intensity. In Equation 1 of the present invention, “around 854 eV” means a region of 854±2.0 eV, and “around 855.5 eV” means a region of 855.5±2.0 eV. In the present invention, “particle surface” means an area within a distance of 100 nm from the surface of the particle toward the center. In the present invention, "D 50 "It refers to the particle size corresponding to 50% of the volume accumulation in the volume accumulation particle size distribution of the target powder, and can be measured using the laser diffraction method. For example, after dispersing the positive active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S-3500), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume accumulation particle size distribution graph, and finding the particle size at the point where the volume accumulation amount is 50% from the obtained graph. Method for manufacturing mixed cathode materials First, a method for manufacturing a mixed cathode material according to the present invention will be described. High-nickel (High Ni) cathode active materials, which contain at least 70 mol% nickel (Ni) among all metals excluding lithium, have the advantage of high capacity. However, they suffer from significant changes in lattice constant, i.e., changes in volume within the unit cell. These volume changes can cause cracks within the active material particles, which can lead to voids within the active material, thereby degrading battery performance. Furthermore, the high nickel content leads to frequent cation mixing between lithium and nickel ions, resulting in the presence of a large amount of lithium byproducts on the surface of the cathode active material particles. These lithium byproducts not only cause gelation of the cathode slurry and swelling of the battery, but also accelerate side reactions with the electrolyte, which can lead to a shortened battery life. Therefore, unlike conventional cathode active materials with a nickel content of less than 70 mol%, high-nickel cathode active materials with a nickel content of 70 mol% or more require a washing process to remove lithium byproducts from the particle surface during the manufacturing process. However, if the washing process is not properly controlled and leads to overwashing, this can lead to surface degradation, which involves the loss of not only the lithium byproducts on the surface but also the lithium that forms the intraparticle structure. This surface degradation can increase resistance and deteriorate cycle life and storage characteristics. Moreover, in the case of a bimodal type cathode material in which large and small particles are mixed, if the washing conditions are set to the large particle standard, there is a problem that the lithium byproducts on the surface of the small particles are not removed enough, causing them to act as a resistor or increasing the amount of gas generated. On the other hand, if the washing conditions are set to the small particle standard, the large particles are washed excessively, causing damage to the surface, which increases the resistance. Accordingly, the inventors of the present invention manufactured a high-nickel bimodal cathode material, including the steps described below, thereby enabling the removal of lithium byproducts without surface degradation through a properly controlled washing process for both large and small particles. This prevented excessive formation of lithium byproducts on the surface, thereby enhancing the surface stability of the cathode material. Furthermore, the inventors confirmed that the lifespan and storage characteristics of batteries containing the cathode material were improved. Below, each step included in the method for manufacturing the mixed cathode material of the present invention is described. a) Step of manufacturing the first sintered body A method for manufacturing a mixed cathode material according to one embodiment of the present invention includes a step of mixing and firing a first precursor containing nickel of 70 mol% or more relative to the total molar number of transition metals and a first lithium source to manufacture a first fired body. At this time, the first precursor may be a transition metal precursor, for example, a commercially available nickel-cobalt-manganese hydroxide, or may be manufactured according to a precursor manufacturing method known in the art. Specifically, the first precursor may be a transition metal hydroxide comprising nickel, cobalt, and manganese, and containing nickel in an amount of at least 70 mol% relative to the total molar number of transition metals. When the nickel content in the precursor satisfies the above range, high capacity characteristics can be realized. Specifically, the first precursor may be represented by the following chemical formula 1-1. [Chemical Formula 1-1] Ni b1 Co c1 Mn d1 Q e1 (OH)2 In the above chemical formula 1-1, b1, c1, d1 and e1 are 0.7≤b1<1.0, 0 respectively <c1<0.3, 0<d1<0.3, 0≤e1≤0.1, b1+c1+d1+e1=1이고, Q is at least one selected from the group consisting of Al, Mg, V, Ti, and Zr. In one embodiment of the present invention, b1, c1, d1 and e1 of the chemical formula 1-1 are 0.7≤b1<1.0, 0, respectively. <c1≤0.15, 0<d1≤0.25 및 0≤e1≤0.05일 수 있으며, 더욱 바람직하게는 0.7≤b1<1.0, 0<c1≤0.1, 0<d1≤0.2 및 0≤e1≤0.03일 수 있다. The first precursor described above and the second precursor described below can be manufactured by, for example, introducing a transition metal aqueous solution and an ammonium cation complex forming and basic compound into a reactor and performing a co-precipitation reaction while stirring. The above transition metal aqueous solution can be prepared by dissolving a transition metal-containing raw material in a solvent such as water. For example, it can be prepared by dissolving a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material in water. In addition, if necessary, the transition metal aqueous solution can further include the Q and Q' metal-containing raw materials. Meanwhile, the above transition metal-containing raw material may be an acetate, carbonate, nitrate, sulfate, halite, sulfide, or oxide of the transition metal. Specifically, the nickel-containing raw material may be, for example, NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halide, or a combination thereof. The above cobalt-containing raw material is, for example, CoSO 4, It can be Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O, CoSO4ㆍ7H2O, or a combination thereof. The manganese-containing raw material may be, for example, Mn2O3, MnO2, Mn3O4MnCO3, Mn(NO3)2, MnSO4ㆍH2O, manganese acetate, manganese halide, or a combination thereof. The above Q, Q' metal-containing raw material may be an aluminum-containing raw material, and may be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halide or a combination thereof. However, in the case of Al, it may not be added to the transition metal aqueous solution, but may be added together with the lithium source in the calcination step described later. In addition, it may be an acetate, carbonate, nitrate, sulfate, halite, sulfide or oxide of the Q, Q' metal. The input amount of each of the above transition metal-containing raw materials can be determined by considering the molar ratio of the transition metal in the positive electrode active material to be ultimately produced. Meanwhile, the ammonium cation complex forming agent may include at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and (NH4)2CO3, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. At this time, the solvent may be water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water. The basic compound may be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. At this time, the solvent may be water, or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water. As described above, when a transition metal aqueous solution, an ammonium cation complex forming agent, and a basic compound are introduced into a reactor and stirred, the transition metals in the transition metal aqueous solution coprecipitate, generating precursor particles in the form of transition metal hydroxides. At this time, the above transition metal aqueous solution, ammonium cation complex forming agent, and basic compound are added in an amount such that the pH of the reaction solution becomes within the desired range. Once precursor particles are formed as described above, the particles are separated from the reaction solution to obtain a transition metal precursor. For example, the reaction solution may be filtered to separate the transition metal precursor, and then the separated transition metal precursor may be washed and dried to obtain the transition metal precursor. Processes such as grinding and / or classification may also be performed as needed. The transition metal precursor obtained in this way is mixed with a first lithium source as a first precursor and then calcined to produce a first lithium transition metal oxide. At this time, Q may be added as needed. Metal-containing raw materials can be mixed and fired together. As the first lithium source, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide may be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or a mixture thereof may be used. Meanwhile, in one embodiment of the present invention, the step of manufacturing the first sintered body may be to mix the first precursor and the first lithium source so that the molar ratio of lithium in the first lithium source to the total metal elements of the first precursor (Li / M)1 is 1.03 to 1.09, preferably 1.03 to 1.06, and more preferably 1.04 to 1.05. When (Li / M)1 is 1.03 or more, the structural completeness is increased, which is preferable. However, if excessive lithium byproducts remain on the surface, it acts as a resistor and the amount of gas generated by residual lithium may increase, so it is preferable that it is 1.09 or less. In one embodiment of the present invention, the sintering in the step of manufacturing the first sintered body may be performed in an oxygen atmosphere at a temperature of 700°C to 900°C, preferably 800°C to 900°C, for 8 to 12 hours. It is preferable that the sintering temperature and time be within the above ranges in order to secure structural stability through sufficient reaction while simultaneously securing optimal electrochemical properties. b) Step of producing a first lithium transition metal oxide A method for manufacturing a mixed cathode material according to one embodiment of the present invention includes a step of manufacturing a first lithium transition metal oxide by washing the first sintered body with 50 to 70 parts by weight of a washing solution based on 100 parts by weight of the first sintered body. In the present invention, the content of the washing liquid based on 100 parts by weight of the first sintered body in the washing process is adjusted to 50 parts by weight to 70 parts by weight, preferably 60 parts by weight to 70 parts by weight, thereby achieving an optimal washing effect in terms of surface characteristics and residual lithium amount. Specifically, when the content of the washing liquid based on 100 parts by weight of the first sintered body is less than 50 parts by weight, excessive residual lithium byproducts remain on the particle surface, which becomes a factor causing problems such as increased side reactions due to the excessive lithium byproducts described above and slurry gelation, and when it exceeds 70 parts by weight, the surface is damaged due to excessive washing. In one embodiment of the present invention, the washing step of producing the first lithium transition metal oxide may be performed by placing the first calcined body in water and stirring at a temperature of 15°C to 25°C and a speed of 1,500 rpm to 2,500 rpm for 1 to 20 minutes. Specifically, the washing can be performed by stirring the first calcined body with water using a magnetic bar in a stirrer, and the temperature during the stirring can be 15°C to 25°C, preferably 15°C to 20°C, and the stirring speed can be 1,500 rpm to 2,500 rpm, preferably 1,500 rpm to 2,000 rpm. After the above washing, a drying step may be performed at a temperature of 130°C to 150°C for 12 to 24 hours, but is not limited thereto. c) Step of manufacturing a second sintered body A method for manufacturing a mixed cathode material according to one embodiment of the present invention includes a step of mixing and firing a second precursor and a second lithium source containing nickel of 70 mol% or more relative to the total moles of transition metals to manufacture a second fired body. At this time, the second precursor may be a transition metal precursor, such as a commercially available nickel-cobalt-manganese hydroxide, or may be manufactured according to a precursor manufacturing method known in the art. Specifically, the second precursor may be a transition metal hydroxide comprising nickel, cobalt, and manganese, and containing nickel in an amount of at least 70 mol% relative to the total molar number of transition metals. When the nickel content in the precursor satisfies the above range, high capacity characteristics can be achieved. Specifically, the second precursor may be represented by the following chemical formula 2-1. [Chemical Formula 2-1] Ni h1 Co i1 Mn j1 Q' k1 (OH)2 In the above chemical formula 2-1, h1, i1, j1 and k1 are 0.7≤h1<1.0, 0 respectively <i1<0.3, 0<j1<0.3, 0≤k1≤0.1, h1+i1+j1+k1=1이고, Q' is at least one selected from the group consisting of Al, Mg, V, Ti, and Zr. In one embodiment of the present invention, h1, i1, j1 and k1 of the chemical formula 2-1 are 0.7≤h1<1.0, 0, respectively. <i1≤0.15, 0<j1≤0.25 및 0≤k1≤0.05일 수 있으며, 더욱 바람직하게는 0.7≤h1<1.0, 0<i1≤0.1, 0<j1≤0.2 및 0≤k1≤0.03일 수 있다. As the second precursor, a transition metal precursor manufactured by the method described in the description of the step of manufacturing the first sintered body may be used, and the second precursor is mixed with a second lithium source and then sintered to manufacture a second lithium transition metal oxide. At this time, Q' may be added as needed. Metal-containing raw materials can be mixed and fired together. As the second lithium source, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide may be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or a mixture thereof may be used. Meanwhile, in one embodiment of the present invention, the step of manufacturing the second sintered body may be to mix the second precursor and the second lithium source so that the molar ratio of lithium in the second lithium source to the total metal elements of the second precursor (Li / M)2 is 1.01 to 1.04, preferably 1.02 to 1.04, and more preferably 1.02 to 1.03. When (Li / M)2 is 1.01 or more, the structural completeness is increased, which is preferable. However, if excessive lithium byproducts remain on the surface, it acts as a resistor and the amount of gas generated by residual lithium may increase, so it is preferable that it is 1.04 or less. In one embodiment of the present invention, the firing in the step of manufacturing the second sintered body may be performed in an oxygen atmosphere at a temperature of 700°C to 900°C, preferably 800°C to 900°C, for 8 to 12 hours. It is preferable that the firing temperature and time be within the above ranges in order to secure structural stability through sufficient reaction while simultaneously securing optimal electrochemical properties. d) Step of producing a second lithium transition metal oxide A method for manufacturing a mixed cathode material according to one embodiment of the present invention includes a step of manufacturing a second lithium transition metal oxide by washing the second sintered body with 60 to 80 parts by weight of a washing solution based on 100 parts by weight of the second sintered body. In the present invention, the content of the washing liquid based on 100 parts by weight of the second sintered body in the washing process is adjusted to 60 parts by weight to 80 parts by weight, preferably 60 parts by weight to 70 parts by weight, thereby achieving an optimal washing effect in terms of surface characteristics and residual lithium amount. Specifically, when the content of the washing liquid based on 100 parts by weight of the second sintered body is less than 60 parts by weight, an excessive amount of residual lithium byproducts remains on the particle surface, which causes problems such as increased side reactions due to the excessive amount of lithium byproducts described above and slurry gelation, and when it exceeds 80 parts by weight, the surface is damaged due to excessive washing. In one embodiment of the present invention, the washing step of producing the second lithium transition metal oxide may be performed by placing the second calcined body in water and stirring at a temperature of 15°C to 25°C and a speed of 1,500 rpm to 2,500 rpm for 1 to 20 minutes. Specifically, the washing can be performed by stirring the second sintered body with water using a magnetic bar in a stirrer, and the temperature during the stirring can be 15°C to 25°C, preferably 15°C to 20°C, and the stirring speed can be 1,500 rpm to 2,500 rpm, more preferably 1,500 rpm to 2,000 rpm. Afterwards, a vacuum drying step may be performed at a temperature of 130°C to 180°C for 12 to 24 hours, but is not limited thereto. In addition, the method for manufacturing a mixed cathode material according to one embodiment of the present invention may further include a step of mixing the first lithium transition metal oxide and the second lithium transition metal oxide in a weight ratio of 6:4 to 8:2, preferably 7:3 to 8:2. It is advantageous for increasing the rolling density to include a larger amount of the first lithium transition metal oxide than the second lithium transition metal oxide. Meanwhile, D of the first lithium transition metal oxide 50 D of the second lithium transition metal oxide 50 As compared to, it may be 8㎛ to 15㎛, preferably 9㎛ to 15㎛, more preferably 9㎛ to 12㎛. In addition, the D of the second lithium transition metal oxide 50 The silver may be 2㎛ to 5㎛, preferably 3㎛ to 5㎛, and more preferably 3㎛ to 4㎛. Meanwhile, in the process of washing the first and second sintered bodies, the washing liquid may be water or a mixture of water and an additive, and preferably may be water. As the washing liquid additive, LiOH, which can replenish lithium ions lost during the washing process, and / or NaOH, which can produce a flux effect, may be used, but the present invention is not limited thereto. mixed cathode materials Next, a mixed cathode material according to the present invention will be described. The mixed cathode material according to the present invention can be manufactured using the manufacturing method of the present invention described above, and the description of each component can be cited from the description of the manufacturing method described above. The mixed cathode material according to the present invention comprises a first cathode active material including a first lithium transition metal oxide and a second cathode active material including a second lithium transition metal oxide, wherein the first lithium transition metal oxide and the second lithium transition metal oxide each have a nickel content of 70 mol% or more among the total metals excluding lithium, and D of the first cathode active material 50 D of the above second positive electrode active material 50 It is larger, and the EELS analysis results for the particle surfaces of the first positive electrode active material and the second positive electrode active material each satisfy the following equation 1. [Formula 1] I(854eV) / I(855.5eV) ≤ 1 In the above equation 1, I(854 eV) is the peak intensity that appears around 854 eV, I(855.5 eV) is the peak intensity that appears around 855.5 eV. From the EELS analysis results, Ni 2+ In the case of Ni, around 854 eV 3+ In the case of Ni, it appears around 855.5 eV, so the intensity of each peak is compared. 2+ and Ni 3+ The content of can be compared. That is, the mixed cathode material satisfying the above formula 1 has Ni on the particle surface, specifically on the particle surface of each of the first cathode active material and the second cathode active material. 3+ Go Ni 2+ There are more of them than there are of the same type. As the surface degradation due to water washing becomes more severe, the NiO phase is formed as the layered structure changes to a rock salt structure, so Ni 2+As the oxidation value of Ni increases, the mixed cathode material according to the present invention has the effect of reducing surface damage due to washing as described above, so that degradation occurs less and can satisfy the above equation 1. Specifically, the I(854eV) / I(855.5eV) value may be 0.85 or more, more specifically 0.90 or more, and 0.99 or less, or 0.95 or less. When the I(854eV) / I(855.5eV) value is 0.85 or more, less lithium compounds remain on the particle surface, so better performance in terms of resistance and lifespan can be achieved. In one embodiment of the present invention, the molar ratio of lithium to all metal elements excluding lithium in the first lithium transition metal oxide may be 1.03 to 1.09, preferably 1.03 to 1.06, and more preferably 1.04 to 1.05. In one embodiment of the present invention, the first lithium transition metal oxide may be a lithium transition metal oxide containing nickel, cobalt, and manganese, and containing nickel in an amount of 70 mol% or more relative to the total molar number of all transition metals. When the nickel content satisfies the above range, high capacity characteristics can be achieved. Specifically, the first lithium transition metal oxide can be represented by the following chemical formula 1. [Chemical Formula 1] Li a Ni b Co c Mn d Q e O 2+f In the above chemical formula 1, a, b, c, d, e and f are 1.01≤a≤1.09, 0.7≤b<1.0, 0 respectively <c<0.3, 0<d<0.3, 0≤e≤0.1, b+c+d+e=1, -0.1≤f≤1.0이고, Q is at least one selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. Preferably, a in the above chemical formula 1 may be 1.02 to 1.06, more preferably 1.03 to 1.05. In one embodiment of the present invention, b, c, d and e of the chemical formula 1 are 0.7≤b<1.0, 0, respectively. <c≤0.15, 0<d≤0.25 및 0≤e≤0.05일 수 있으며, 더욱 바람직하게는 0.7≤b<1.0, 0<c≤0.1, 0<d≤0.2 및 0≤e≤0.03일 수 있다. In one embodiment of the present invention, the first positive electrode active material is in the form of secondary particles in which a plurality of primary particles are aggregated, D 50 The silver may be 8㎛ to 15㎛, preferably 9㎛ to 15㎛, and more preferably 9㎛ to 12㎛. D 50 Although it is desirable for the particle size to be 8㎛ or larger to increase the rolling density, if the particle size is too large, it may pierce the current collector foil during rolling, leading to electrode short circuits, etc., so it is desirable that it does not exceed 15㎛. In one embodiment of the present invention, the molar ratio of lithium to all metal elements excluding lithium in the second lithium transition metal oxide may be 1.01 to 1.04, preferably 1.02 to 1.04, and more preferably 1.02 to 1.03. In one embodiment of the present invention, the first lithium transition metal oxide may be a lithium transition metal oxide containing nickel, cobalt, and manganese, and containing nickel in an amount of 70 mol% or more relative to the total molar number of all transition metals. When the nickel content satisfies the above range, high capacity characteristics can be achieved. Specifically, the second lithium transition metal oxide can be represented by the following chemical formula 2. [Chemical Formula 2] Li g Ni h Co i Mn j Q' k O 2+q In the above chemical formula 2, g, h, i, j, k and q are 1.01≤g≤1.04, 0.7≤h<1.0, 0, respectively. <i<0.3, 0<j<0.3, 0≤k≤0.1, h+i+j+k=1, -0.1≤q≤1.0이고, Q' is at least one selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. Preferably, g in the above chemical formula 2 may be 1.02 to 1.04, more preferably 1.02 to 1.03. In one embodiment of the present invention, h, i, j and k of the chemical formula 1 are 0.7≤b<1.0, 0, respectively. <c≤0.15, 0<d≤0.25 및 0≤e≤0.05일 수 있으며, 더욱 바람직하게는 0.7≤b<1.0, 0<c≤0.1, 0<d≤0.2 및 0≤e≤0.03일 수 있다. In one embodiment of the present invention, the second positive electrode active material is in the form of secondary particles in which a plurality of primary particles are aggregated, D 50 The size of the particles may be 2 ㎛ to 5 ㎛, preferably 3 ㎛ to 5 ㎛, and more preferably 3 ㎛ to 4 ㎛. If the size of the particles in the bimodal cathode material becomes too small, the rolling density may decrease and the amount of gas generated by the fine particles may increase, so D 50 Although it is desirable that it be 3㎛ or more, considering the purpose of implementing the optimal rolling density by taking into account the bimodal effect with the opposing party, it is desirable that it does not exceed 5㎛. anode Next, the anode according to the present invention will be described. The positive electrode according to the present invention comprises the above-described mixed positive electrode material. Specifically, the positive electrode comprises: a positive electrode current collector; and a positive electrode active material layer provided on the positive electrode current collector and comprising the above-described mixed positive electrode material. In the above positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric. In addition, the positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material described above. The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. Specific examples include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; carbon-based materials such as carbon fibers and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types of these may be used. The conductive material may typically be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the positive electrode active material layer. The above binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above binder may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the positive electrode active material layer. The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method. For example, the positive electrode can be manufactured by mixing a positive electrode active material, a binder, and / or a conductive agent in a solvent to prepare a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above. The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode. Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry onto a separate support, then peeling the resulting film from the support and laminating it onto a positive electrode current collector. lithium secondary battery Next, a lithium secondary battery according to the present invention will be described. The lithium secondary battery of the present invention comprises the positive electrode, the negative electrode including the negative electrode active material, the separator interposed between the positive electrode and the negative electrode, and the electrolyte. In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container. The above negative electrode includes a negative electrode current collector; and a negative electrode active material layer provided on the negative electrode current collector and including a negative electrode active material. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β (0 <β< 2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes. Preferably, the negative electrode active material may be graphite, SiO or a mixture thereof. The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. Specific examples include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; carbon-based materials such as carbon fibers and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may typically be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the negative electrode active material layer. The above binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used. The above binder may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the negative electrode active material layer. The above-described negative electrode active material layer may be manufactured by, for example, applying a negative electrode slurry containing a negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode slurry onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling it off from the support. Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator used as a separator in a typical lithium secondary battery can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, 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, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material can be used to secure heat resistance or mechanical strength, and can optionally be used in a single-layer or multi-layer structure. Meanwhile, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may include an organic solvent and a lithium salt. The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable. The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 5.0 M, and preferably 0.1 to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively. In addition to the electrolyte components, the electrolyte may further include additives for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. For example, the additives may include haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, which may be used alone or in combination, but are not limited thereto. The additives may be included in an amount of 0.1 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%, based on the total weight of the electrolyte. As described above, a lithium secondary battery including a cathode material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided. The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system. Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. [Examples and Comparative Examples: Manufacturing of Cathode Materials] Example 1. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.03, and the first sintered body was manufactured by heat-treating at 870°C for 10 hours under an oxygen atmosphere. After that, 60 g of the manufactured first sintered body was placed in a beaker containing 40 g of water, placed on a stirrer, and stirred at 2,000 rpm for 10 minutes at 15°C, thereby performing washing. After washing, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.03 [Ni 0.7 Co 0.1 Mn 0.2]O2 was prepared. The prepared first lithium transition metal oxide was used as a first positive electrode active material, and its D 50 was 10㎛. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.03, and heat-treated at 860°C for 10 hours under an oxygen atmosphere to prepare a second sintered body. After that, 60 g of the prepared second sintered body was placed in a beaker containing 40 g of water, placed on a stirrer, and stirred at 2,000 rpm for 10 minutes at 15°C, thereby performing washing. After washing, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.03 [Ni 0.7 Co 0.1 Mn 0.2 ]O2 composition was prepared. The prepared second lithium transition metal oxide was used as a second positive electrode active material, and its D 50 was 4㎛. Thereafter, the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to manufacture a mixed positive electrode material. Example 2. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.05, and the first sintered body was manufactured by heat-treating at 870°C for 10 hours under an oxygen atmosphere. After that, 60 g of the manufactured first sintered body was placed in a beaker containing 40 g of water, placed on a stirrer, and stirred at 1,500 rpm for 10 minutes at 15°C, thereby performing washing. After washing, the first sintered body was dried by vacuum drying at 130°C for 24 hours, and Li 1.05 [Ni 0.7 Co 0.1 Mn 0.2]O2 was prepared. The prepared first lithium transition metal oxide was used as a first positive electrode active material, and its D 50 was 10㎛. The second positive electrode active material was manufactured using the same process as in Example 1. Thereafter, the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to manufacture a mixed positive electrode material. Comparative Example 1. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.00, and heat-treated at 870°C in an oxygen atmosphere for 10 hours to prepare a first sintered body. After that, 40 g of the first sintered body was placed in a beaker containing 60 g of water, placed on a stirrer, and stirred at 1,500 rpm for 10 minutes at 15°C to perform washing. After washing, the first sintered body was dried by vacuum drying at 130°C for 24 hours, and Li 1.00 [Ni 0.7 Co 0.1 Mn 0.2 ]O2 was prepared. The prepared first lithium transition metal oxide was used as a first positive electrode active material, and its D 50 was 10㎛. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.00, and heat-treated at 860°C in an oxygen atmosphere for 10 hours to produce a second sintered body. After that, 40 g of the first sintered body was placed in a beaker containing 60 g of water, placed on a stirrer, and stirred at 1,500 rpm for 10 minutes at 15°C to perform washing. After washing, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.00 [Ni0.7 Co 0.1 Mn 0.2 ]O2 composition was prepared. The prepared second lithium transition metal oxide was used as a second positive electrode active material, and its D 50 was 4㎛. Thereafter, the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to manufacture a mixed positive electrode material. Comparative Example 2. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.12, and heat-treated at 870°C in an oxygen atmosphere for 10 hours to prepare a first sintered body. After that, 60 g of the first sintered body was placed in a beaker containing 40 g of water, placed on a stirrer, and stirred at 1,500 rpm for 10 minutes at 15°C to perform washing. After washing, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.12 [Ni 0.7 Co 0.1 Mn 0.2 ]O2 was prepared. The prepared first lithium transition metal oxide was used as a first positive electrode active material, and its D 50 was 10㎛. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.10, and heat-treated at 860°C in an oxygen atmosphere for 10 hours to produce a second sintered body. After that, 60 g of the first sintered body was placed in a beaker containing 40 g of water, placed on a stirrer, and stirred at 1,500 rpm for 10 minutes at 15°C to perform washing. After washing, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.10 [Ni 0.7 Co0.1 Mn 0.2 ]O2 composition was prepared. The prepared second lithium transition metal oxide was used as a second positive electrode active material, and its D 50 was 4㎛. Thereafter, the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to manufacture a mixed positive electrode material. Comparative Example 3. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.03, and the first sintered body was manufactured by heat-treating at 870°C for 10 hours under an oxygen atmosphere. After that, 50 g of the manufactured first sintered body was placed in a beaker containing 50 g of water, placed on a stirrer, and stirred at 2,000 rpm for 10 minutes at 15°C, thereby performing washing. After washing, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.03 [Ni 0.7 Co 0.1 Mn 0.2 ]O2 was prepared. The prepared first lithium transition metal oxide was used as a first positive electrode active material, and its D 50 was 10㎛. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the Li / M(Ni+Co+Mn) molar ratio was 1.03, and heat-treated at 870°C for 10 hours under an oxygen atmosphere to prepare a second sintered body. After that, 50 g of the prepared second sintered body was placed in a beaker containing 50 g of water, placed on a stirrer, and stirred at 2,000 rpm for 10 minutes at 15°C, thereby performing washing. After washing, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.03 [Ni 0.7 Co 0.1 Mn0.2 ]O2 composition was prepared. The prepared second lithium transition metal oxide was used as a second positive electrode active material, and its D 50 was 4㎛. Thereafter, the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to manufacture a mixed positive electrode material. Comparative Example 4. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.00, and the first sintered body was manufactured by heat-treating at 870°C for 10 hours under an oxygen atmosphere. After that, 40 g of the manufactured first sintered body was placed in a beaker containing 60 g of water, placed on a stirrer, and stirred at 2,000 rpm for 10 minutes at 15°C, thereby performing washing. After washing, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.00 [Ni 0.7 Co 0.1 Mn 0.2 ]O2 was prepared. The prepared first lithium transition metal oxide was used as a first positive electrode active material, and its D 50 was 10㎛. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / M(Ni+Co+Mn) was 1.07, and heat-treated at 870°C for 10 hours under an oxygen atmosphere to prepare a second sintered body. After that, 70 g of the prepared second sintered body was placed in a beaker containing 30 g of water, placed on a stirrer, and stirred at 2,000 rpm for 5 minutes at 15°C to perform washing. After washing, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.07 [Ni 0.7 Co 0.1 Mn 0.2]O2 composition was prepared. The prepared second lithium transition metal oxide was used as a second positive electrode active material, and its D 50 was 4㎛. Thereafter, the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to manufacture a mixed positive electrode material. [Experimental Example: EELS Analysis and Performance Evaluation] Experimental Example 1. EELS Analysis For each of the mixed cathode materials manufactured in the above examples and comparative examples, a TEM device (FEI Ttitan G2 80-200 ChemiSTEM) was used to analyze up to 100 nm from the particle surface in EELS mode to obtain a spectrum, and the results are shown in Figs. 1 to 4. Figs. 1 and 3 show the results of analyzing the first cathode active material particles in each mixed cathode material, and Figs. 2 and 4 show the results of analyzing the second cathode active material particles. After confirming the peak intensity appearing at 854 eV and the peak intensity appearing at 855.5 eV in the corresponding spectra, I(854 eV) / I(855.5 eV) was calculated and shown in Table 1 below. Experimental Example 2. Resistance and Life Evaluation (1) Manufacturing of half-cells The mixed cathode material, conductive material (carbon black), and binder (PVDF) manufactured in the above examples and comparative examples were mixed in a weight ratio of 96:2:2 in N-methylpyrrolidone to manufacture a cathode slurry. The cathode slurry was applied to one surface of an aluminum current collector, dried at 100°C, and then rolled to manufacture a cathode. An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive electrode and the lithium metal negative electrode, and then positioning it inside a battery case, and then injecting an electrolyte into the case to manufacture a half cell. The electrolyte was manufactured by dissolving 1 M LiPF6 in a mixed organic solvent containing ethylene carbonate / dimethyl carbonate / diethyl carbonate in a volume ratio of 3:4:3. (2) Initial resistance measurement For each of the above-mentioned manufactured half-cells, an activation (formation) process was performed, and then the cells were charged under constant current-constant voltage conditions at 0.33C rate at 25℃ using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd.), discharged at 0.33C to reach 50% SOC, and then the voltage drop that occurred while applying a discharge pulse at 2.5C constant current for 10 seconds was measured to obtain the initial resistance value. This is shown in Table 1 below. (3) Life span measurement For each of the above-manufactured half-cells, a constant current-constant voltage charge (0.05C cut off) was performed at 45°C at a 1C rate to 4.3 V, and a constant current (CC) discharge to 3.0 V at a 1C rate was defined as one cycle. After repeating the same charge / discharge 100 times, the capacity retention rate was measured using the following equation. The measurement results are shown in Table 1 below. - Capacity retention rate (%) = (discharge capacity after 100 cycles / discharge capacity after 1 cycle) × 100 (4) Gas measurement Each of the above-manufactured half-cells was charged in CCCV mode at a rate of 0.1 C until the voltage reached 4.3 V (end current 1 / 20 C). After charging, the cell was disassembled to obtain two charged positive electrodes and two polyethylene separators. The positive electrodes and separators were alternately stacked on the lower plate of the coin cell, electrolyte was injected, and the coin cell was reassembled. After storage at 70 ° C for 4 weeks, the amount of gas generated was measured using a gas chromatograph-mass spectrometer (GC-MS). Experimental Example 1 Experimental Example 2 First positive electrode active material Second positive electrode active material Initial resistance (Ω) Capacity retention rate (%) Gas generation amount (㎕) Example 10.90 0.92 1.38 95.910 2 Example 20.95 0.93 1.36 96.11 15 Comparative Example 11.62 1.41 1.65 88.210 6 Comparative Example 21.40 1.28 1.53 89.714 3 Comparative Example 31.52 1.38 1.59 88.1107 Comparative Example 41.62 0.80 1.61 87.810 6 Through the results in Table 1 above, it can be confirmed that when a mixed cathode material is used in which both the first cathode active material and the second cathode active material satisfy Equation 1, it is effective in lowering the initial resistance, improving the lifespan, and lowering the amount of gas generated. On the other hand, in the case of Comparative Example 1 in which the first sintered body and the second sintered body were washed with 150 parts by weight of a washing solution per 100 parts by weight of the sintered body during the cathode material manufacturing process, and in Comparative Example 3 in which the first sintered body and the second sintered body were washed with 100 parts by weight of a washing solution per 100 parts by weight of the sintered body, it can be confirmed that the surface damage was aggravated due to excessive washing, and as a result, the Ni oxidation value was lowered, failing to satisfy Equation 1, and the initial resistance and lifespan characteristics were deteriorated. Meanwhile, in the case of Comparative Example 2, the excess lithium was not properly calcined, so the surface was formed as a rock salt structure rather than a layered structure, and Ni was formed due to the NiO phase. 2+Since there are many lithium byproducts, Equation 1 is not satisfied, and as a result, the initial resistance and life characteristics are confirmed to be deteriorated. In particular, it can be confirmed that the amount of gas generated also increases significantly due to the excess lithium byproduct remaining on the surface. In addition, in the case of Comparative Example 4, the second positive electrode active material satisfies Equation 1, but in the case of the first positive electrode active material, the Ni oxidation value is low due to excessive water washing during the manufacturing process, so it is confirmed that the initial resistance and life characteristics are poor because it does not satisfy Equation 1.

Claims

1. A first positive electrode active material comprising a first lithium transition metal oxide and a second positive electrode active material comprising a second lithium transition metal oxide, The above first lithium transition metal oxide and the above second lithium transition metal oxide each have a nickel content of 70 mol% or more among the total metals excluding lithium, D of the above first positive electrode active material 50 D of the above second positive electrode active material 50 It is bigger than, A mixed cathode material, wherein the EELS analysis results for the particle surfaces of the first cathode active material and the second cathode active material satisfy the following equation 1: [Formula 1] I(854eV) / I(855.5eV) < 1 In the above equation 1, I(854 eV) is the peak intensity that appears around 854 eV, I(855.5 eV) is the peak intensity that appears around 855.5 eV.

2. In claim 1, A mixed cathode material having an I(854 eV) / I(855.5 eV) value of the above formula 1 of 0.85 or more.

3. In claim 1, A mixed cathode material, wherein the molar ratio of lithium to all metal elements excluding lithium in the first lithium transition metal oxide is 1.01 to 1.

09.

4. In claim 1, A mixed cathode material, wherein the molar ratio of lithium to all metal elements excluding lithium in the second lithium transition metal oxide is 1.01 to 1.

04.

5. In claim 1, A mixed cathode material, wherein the weight ratio of the first cathode active material and the second cathode active material is 6:4 to 8:

2.

6. In claim 1, The above first lithium transition metal oxide is a mixed cathode material represented by the following chemical formula 1: [Chemical Formula 1] Li a Ni b Co c Mr d Q e O 2+f In the above chemical formula 1, a, b, c, d, e and f are 1.01≤a≤1.09, 0.7≤b<1.0, 0 respectively <c<0.3, 0<d<0.3, 0≤e≤0.1, b+c+d+e=1, -0.1≤f≤1.0이고, Q is at least one selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

7. In claim 1, The second lithium transition metal oxide is a mixed cathode material represented by the following chemical formula 2: [Chemical Formula 2] Li g Ni h Co i Mr j Q' k O 2+q In the above chemical formula 2, g, h, i, j, k and q are 1.01≤g≤1.04, 0.7≤h<1.0, 0, respectively. <i<0.3, 0<j<0.3, 0≤k≤0.1, h+i+j+k=1, -0.1≤q≤1.0이고, Q' is at least one selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

8. In claim 1, D of the above first positive electrode active material 50 This mixed cathode material is 8㎛ to 15㎛.

9. In claim 1, D of the above second positive electrode active material 50 This mixed cathode material is 2㎛ to 5㎛.

10. A step of mixing and calcining a first precursor containing nickel of 70 mol% or more based on the total moles of transition metals and a first lithium source to produce a first calcined body; A step of manufacturing a first lithium transition metal oxide by washing the first sintered body with 50 to 70 parts by weight of a washing solution based on 100 parts by weight of the first sintered body; A step of mixing and firing a second precursor containing nickel of 70 mol% or more based on the total moles of transition metals and a second lithium source to produce a second sintered body; and A step of manufacturing a second lithium transition metal oxide by washing the second sintered body with 60 to 80 parts by weight of a washing solution based on 100 parts by weight of the second sintered body, D of the above first lithium transition metal oxide 50 D of the above second lithium transition metal oxide 50 A method for producing a mixed cathode material according to claim 1, which is larger than that of the cathode material.

11. In claim 10, A method for producing a mixed cathode material, wherein the step of producing the first sintered body comprises mixing the first precursor and the first lithium source so that the molar ratio of lithium in the first lithium source to the total metal elements of the first precursor (Li / M)1 is 1.03 to 1.

09.

12. In claim 10, A method for producing a mixed cathode material, wherein the step of producing the second sintered body comprises mixing the second precursor and the second lithium source so that the molar ratio of lithium in the second lithium source to the total metal elements of the second precursor (Li / M)2 is 1.01 to 1.

04.

13. In claim 10, A method for producing a mixed cathode material, further comprising a step of mixing the first lithium transition metal oxide and the second lithium transition metal oxide in a weight ratio of 6:4 to 8:

2.

14. In claim 10, A method for producing a mixed cathode material, wherein the washing step of producing the first lithium transition metal oxide is performed by placing the first sintered body in water and stirring it at a temperature of 15°C to 25°C and a speed of 1,500 rpm to 2,500 rpm for 1 to 20 minutes.

15. In claim 10, A method for producing a mixed cathode material, wherein the washing step of producing the second lithium transition metal oxide is performed by placing the second sintered body in water and stirring it at a temperature of 15°C to 25°C and a speed of 1,500 rpm to 2,500 rpm for 1 to 20 minutes.

16. In claim 10, A method for producing a mixed cathode material, wherein the firing in the step of producing the first sintered body is performed at 700°C to 900°C.

17. In claim 10, A method for producing a mixed cathode material, wherein the firing in the step of producing the second sintered body is performed at 700°C to 900°C.

18. A cathode comprising the mixed cathode material of claim 1.

19. A lithium secondary battery comprising: the positive electrode of claim 18; a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

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