Title of Invention: Cathode material for lithium secondary battery, positive electrode and lithium secondary battery including same technical field [One] [Citation with related applications] [2] This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0158017 filed on December 10, 2018, and all contents disclosed in the Korean Patent Application are incorporated as a part of this specification. [3] [4] [Technical field] [5] The present invention relates to a cathode material for a lithium secondary battery, a cathode and a lithium secondary battery including the same. [6] background [7] As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low self-discharge rate has been commercialized and widely used. [8] A lithium transition metal composite oxide is used as a cathode active material for a lithium secondary battery, and among them , a lithium cobalt composite metal oxide such as LiCoO 2 having a high operating voltage and excellent capacity characteristics is mainly used. However, LiCoO 2 has very poor thermal properties due to the destabilization of the crystal structure due to delithiation and is expensive, so there is a limit to its mass use as a power source in fields such as electric vehicles. [9] As a material for replacing the LiCoO 2 , lithium manganese oxide (LiMnO 2 or LiMn 2 O 4, etc.), lithium iron phosphate compound (LiFePO 4 etc.), or lithium nickel oxide (LiNiO 2 etc.) has been developed. Among them, research and development on lithium nickel oxide, which has a high reversible capacity of about 200 mAh/g, and is easy to implement in a large-capacity battery, is being studied more actively. However, the LiNiO 2 has inferior thermal stability compared to LiCoO 2 , and when an internal short circuit occurs due to external pressure in a charged state, the positive electrode active material itself is decomposed, resulting in rupture and ignition of the battery. Accordingly , as a method for improving low thermal stability while maintaining excellent reversible capacity of LiNiO 2 , lithium nickel cobalt manganese oxide in which a part of Ni is substituted with Mn and Co has been developed. [10] However, in the case of the lithium nickel cobalt manganese oxide, the rolling density of the particles is low, and in particular, when the content of Ni is increased to increase the capacity characteristics, the rolling density of the particles is further lowered and the energy density is lowered. When the electrode is strongly rolled to increase the rolling density, there is a problem in that the current collector is broken and the cathode material is cracked. [11] In addition, in the case of lithium nickel cobalt manganese oxide having a high Ni content, there is a problem in that electrochemical performance such as high temperature life is deteriorated due to poor structural stability at high temperature. [12] Accordingly, there is a demand for the development of a cathode material having excellent energy density and capacity characteristics and excellent high temperature lifespan characteristics. [13] [14] [Prior art literature] [15] Korean Patent Publication No. 10-2016-0075196 [16] DETAILED DESCRIPTION OF THE INVENTION technical challenge [17] The present invention is to solve the above problems, and provides a positive electrode material having high rolling density, excellent energy density and capacity characteristics, excellent high temperature life characteristics and continuous charging characteristics, and a positive electrode and a lithium secondary battery including the same want to [18] means of solving the problem [19] In one aspect, the present invention provides a positive electrode material having a bimodal particle size distribution including large particle diameter particles and small particle diameter particles having different average particle diameters (D 50 ), wherein the large particle diameter particles have a nickel content of 80 atm in the total transition metal % or more of a lithium composite transition metal oxide, and the small particle size particles include nickel, cobalt, and aluminum, and the content of nickel in the total transition metal is 80 atm% to 85 atm%, and the atomic ratio of cobalt to aluminum (Co /Al) provides a cathode material of a lithium composite transition metal oxide of 1.5 to 5. [20] [21] In another aspect, the present invention provides a positive electrode comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode material according to the present invention. [22] [23] In another aspect, the present invention, the positive electrode according to the present invention; cathode; a separator interposed between the anode and the cathode; And it provides a lithium secondary battery comprising an electrolyte. [24] Effects of the Invention [25] The positive electrode material of the present invention includes large particle diameter particles and small particle diameter particles having different average particle diameters (D 50 ), and the small particle diameter particles are filled in the voids between the large particle diameter particles, so that it is possible to coat with a high rolling density during electrode coating. Due to this, excellent energy density can be realized. [26] In addition, the positive electrode material of the present invention is a high-nickel positive electrode material having a nickel content of 80 atm% or more, and has excellent capacity characteristics and at the same time uses small particle diameter particles containing nickel, cobalt and aluminum in a specific ratio. Excellent high-temperature life characteristics and continuous charging performance can be realized. [27] Brief description of the drawing [28] 1 is a graph showing evaluation results according to differential scanning calorimetry of the cathode materials of Examples 1 to 3 and Comparative Examples 1 to 5; [29] 2 is a graph showing the evaluation result of the amount of leakage current during continuous charging evaluated according to Experimental Example 2. [30] 3 is a graph showing the high temperature life characteristics evaluated according to Experimental Example 3. [31] Best mode for carrying out the invention [32] The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention. [33] In the present specification, the average particle size (D 50 ) may be defined as a particle size based on 50% of the particle size distribution, and may be measured using a laser diffraction method. Specifically, the average particle diameter (D 50 ) is, after dispersing the target particles in a dispersion medium, introduced into a commercially available laser diffraction particle size measuring device (eg Microtrac MT 3000) and irradiated with ultrasonic waves of about 28 kHz with an output of 60 W , the average particle diameter (D 50 ) on the basis of 50% of the cumulative particle volume distribution according to the particle diameter in the measuring device can be calculated. [34] In the present specification, the content of each element in the lithium composite transition metal oxide can be measured through ICP (Inductive Coupled Plasma) analysis using an inductively coupled plasma emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer). [35] In this specification, % means % by weight unless otherwise specified. [36] [37] As a result of repeated research to develop a cathode material with excellent capacity characteristics, energy density, and high temperature lifespan characteristics, the present inventors have produced lithium composite transition metal oxide with a high nickel content as large particle size particles in a cathode material having a bimodal particle size distribution. In the case of using a lithium composite transition metal oxide having a specific composition as small particle size particles, it was found that the above object can be achieved and the present invention has been completed. [38] [39] cathode material [40] First, a cathode material according to the present invention will be described. [41] The positive electrode material according to the present invention is a positive electrode material having a bimodal particle size distribution including large particle diameter particles and small particle diameter particles having different average particle diameters (D 50 ). It is a lithium composite transition metal oxide, and the small particle size particles include nickel, cobalt, and aluminum, and the content of nickel in the total transition metal is 80 atm% to 85 atm%, and the atomic ratio of cobalt to aluminum (Co/Al) ) is a lithium composite transition metal oxide of 1.5 to 5. [42] [43] As in the present invention, when mixing large particle diameter particles and small particle diameter particles having different average particle diameters (D 50 ), small particle diameter particles are filled in the voids between large particle diameter particles, so particles having one type of average particle diameter are used. It is possible to coat the electrode with a relatively high rolling density compared to the case where it is possible to increase the energy density of the electrode. [44] [45] Meanwhile, in the present invention, a lithium composite transition metal oxide having a nickel content of 80atm% to 85amt% and satisfying a specific composition ratio of aluminum and cobalt is used as the small particle size particles. Specifically, the small particle size particles include nickel, cobalt, and aluminum, the content of nickel in the total transition metal is 80atm% to 85atm%, and the atomic ratio of cobalt to aluminum (Co/Al) is 1.5 to 5 , preferably 1.7 to 5, more preferably 1.7 to 3 lithium composite transition metal oxide. [46] [47] According to the research of the present inventors, it was found that when lithium composite transition metal oxide satisfying the above composition is used as small particle diameter particles, high capacity characteristics, high temperature stability and continuous charging characteristics can be improved at the same time. [48] Specifically, it was found that when the nickel content of the small particle size particles was less than 80 atm%, the capacity characteristics were lowered, and when it exceeded 85 atm%, the high-temperature stability and continuous charging characteristics were lowered. In addition, even when the nickel content of the small particle size particles satisfies 80atm% to 85atm%, when the atomic ratio of cobalt to aluminum (Co/Al) is less than 1.5 or more than 5, the high temperature lifespan characteristics and continuous charging characteristics are lowered appeared to be That is, when the small particle size particles satisfying the specific composition of the present invention are used, capacity characteristics, high temperature stability, and continuous charging characteristics are all excellent. [49] [50] In the present invention, the small particle size particle may be, for example, a lithium composite transition metal oxide represented by the following [Formula 1]. [51] [Formula 1] [52] Li x [Ni y Co z Al w M 1 v ]O 2 [53] In Formula 1, M 1 is Mn, W, Cu, Fe, Ba, V, Cr, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce , Nb, Mg, B, and at least one selected from the group consisting of Mo, preferably Mn, 0.9≤x≤1.5, 0.8≤y≤0.85, 0 [97] The positive electrode material according to the present invention as described above can be usefully used in manufacturing the positive electrode of a lithium secondary battery. [98] Specifically, the positive electrode according to the present invention includes the above-described positive electrode material according to the present invention. More specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer may include the positive electrode material according to the present invention. Since the specific content of the positive electrode material according to the present invention is the same as described above, a detailed description thereof will be omitted. [99] [100] The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode material according to the present invention as the positive electrode active material. For example, the positive electrode is prepared by dissolving or dispersing the components constituting the positive electrode active material layer, that is, the positive electrode material, the conductive material and/or the binder in a solvent, and the positive electrode mixture is used as the positive electrode current collector. It can be prepared by coating on at least one surface, followed by drying and rolling, or by casting the positive electrode composite material on a separate support and then laminating a film obtained by peeling from the support on the positive electrode current collector. [101] In this case, the positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or carbon, nickel on the surface of aluminum or stainless steel. , titanium, silver or the like surface-treated may be used. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body. [102] A positive electrode active material layer comprising the positive electrode material according to the present invention on at least one surface of the current collector, and optionally further containing at least one of a conductive material and a binder, if necessary, is positioned. [103] The cathode material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98 wt%, based on the total weight of the cathode active material layer. When included in the above content range, excellent capacity characteristics may be exhibited. [104] The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it does not cause chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; 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 a conductive polymer such as a polyphenylene derivative, and the like, and one type alone or a mixture of two or more types thereof may be used. The conductive material may be included in an amount of 1 wt% to 30 wt% based on the total weight of the cathode active material layer. [105] In addition, the binder serves to improve the adhesion between the positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used. 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. [106] On the other hand, the solvent used in the preparation of the positive electrode composite material may be a solvent generally used in the art, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N- methyl pyrrol Money (NMP), acetone (acetone), water, etc. may be used alone or a mixture thereof. The amount of the solvent used may be appropriately adjusted in consideration of the application thickness of the slurry, the production yield, the viscosity, and the like. [107] [108] Next, a secondary battery according to the present invention will be described. [109] A secondary battery according to the present invention includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode according to the present invention described above. [110] Meanwhile, the secondary battery may optionally further include a battery container for accommodating the electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container. [111] In the secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector. [112] The negative electrode may be manufactured according to a conventional negative electrode manufacturing method generally known in the art. For example, the negative electrode is prepared by dissolving or dispersing the components constituting the negative electrode active material layer, that is, the negative electrode active material, the conductive material and/or the binder in a solvent, and the negative electrode mixture is used as the negative electrode current collector. It can be prepared by coating on at least one surface, followed by drying and rolling, or by casting the negative electrode composite material on a separate support and then laminating the film obtained by peeling from the support on the negative electrode current collector. [113] The anode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface. Carbon, nickel, titanium, one surface-treated with silver, an aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body. [114] As the anode 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; metal 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 v (0 [160] The positive electrode material, carbon black conductive material, and PVdF binder prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were mixed in an N-methylpyrrolidone solvent in a weight ratio of 96.5:1.5:2.0 to prepare a positive electrode composite material Then, it was coated on one surface of an aluminum current collector, dried at 130° C., and rolled to prepare a positive electrode. [161] As the negative electrode, lithium metal was used. [162] An electrode assembly is prepared by interposing a separator of porous polyethylene between the positive electrode and the negative electrode prepared as described above, the electrode assembly is placed inside the case, and the electrolyte is injected into the case to prepare a coin half cell did. [163] At this time, the electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF 6 ) at a concentration of 1.0 M in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3 / 4 / 3) did. [164] [165] Experimental Example 1: DSC evaluation [166] As described above, a current of 0.2 C was applied to each of the coin half cells prepared using the cathode materials of Examples 1 to 3 and Comparative Examples 1 to 5, charged to 4.25 V, discharged to 2.5 V, and then again 4.25 It was fully charged with a current of 0.2C to V. Then, the positive electrode was recovered by disassembling the fully charged coin cell, and the recovered positive electrode was washed with dimethyl carbonate for 30 seconds to remove the electrolyte remaining on the electrode surface and dried. The dried electrode was punched out according to the size of the pan of the differential scanning calorimetry device (HP-DSC manufactured by Setaram), and 20 μL of the same electrolyte as that of the coin cell was put into the pan, and then the pan was sealed. . Then, the calorific value was measured while the temperature was increased from 25°C to 400°C at a rate of 10°C per minute. [167] The measurement results are shown in FIG. 1 . As shown in FIG. 1 , the cathode materials of Examples 1 to 3 had excellent thermal stability with an exothermic start temperature of 225° C. or higher. appeared to be [168] On the other hand, the cathode material of Comparative Example 1 using small particle size particles not containing Al, Comparative Example 3 using small particle size particles having an atomic ratio of cobalt to aluminum (Co/Al) greater than 5, and Ni content of 85 atm% In the case of the positive electrode material of Comparative Example 5 using particles having a smaller particle size or larger, the heating start temperature was lower than that of the positive electrode materials of Examples 1 to 3, indicating that thermal stability was poor. [169] [170] On the other hand, in the case of the positive electrode materials of Comparative Examples 2 and 4, it was found to have a similar level of thermal stability to the positive electrode material of Examples. [171] [172] Experimental Example 2: Continuous charging evaluation [173] The amount of current leakage during continuous charging was measured for the coin half cells manufactured using the cathode materials of Examples 1 to 3 and Comparative Examples 1 to 5. Specifically, after charging and discharging the coin half-cell at 50°C under 0.2C/0.2C conditions, it is charged at 0.2C until it becomes 4.7V in CC-CV mode, and after setting the end to 120 hours, The average leakage current was obtained by dividing the capacity by the time. The measurement results are shown in FIG. 2 . [174] [175] As shown in FIG. 2 , it can be confirmed that the amount of leakage current during continuous charging of the coin half cells using the cathode materials of Examples 1 to 3 is lower than that of the coin half cells using the cathode materials of Comparative Examples 1 to 5. [176] [177] Experimental Example 3: High-Temperature Lifetime Characteristics [178] [179] Each of the positive electrode material, carbon black conductive material and PVdF binder prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was mixed in an N-methylpyrrolidone solvent in a weight ratio of 96.5:1.5:2.0 to prepare a positive electrode composite material. manufactured, coated on one side of an aluminum current collector, dried at 130° C., and rolled to prepare a positive electrode. [180] A negative electrode mixture was prepared by mixing a negative electrode active material, a binder, and a conductive material in a N-methylpyrrolidone solvent in a weight ratio of 95.6:3.4:1.0. In this case, natural graphite and artificial graphite were mixed in a weight ratio of 9: 1 as a negative active material, BML302 (Xeon Corporation) as a binder, and Super C-65 (Timcal Corporation) as a conductive material were used. The prepared negative electrode mixture was applied to a copper current collector, dried at 130° C., and then rolled to prepare a negative electrode. [181] A separator was interposed between the positive electrode and the negative electrode prepared as described above, and an electrolyte solution was injected to prepare a lithium secondary battery. [182] [183] The lifespan characteristics of the lithium secondary battery prepared as described above were evaluated according to the following method. [184] Charge the lithium secondary battery at 45°C at 0.33C until it becomes 4.2V, discharge it at a constant current of 0.33C until it becomes 2.5V, perform 100 charge/discharge cycles, and 100 cycles compared to the discharge capacity after one cycle The subsequent discharge capacity retention rate was measured. The measurement results are shown in FIG. 3 . [185] As shown in FIG. 3 , it can be seen that the lifespan characteristics of the lithium secondary batteries using the cathode materials of Examples 1 to 3 are superior to those of the lithium secondary batteries using the cathode materials of Comparative Examples 1 to 5. Claims [Claim 1] A positive electrode material having a bimodal particle size distribution including large particle diameter particles and small particle diameter particles having different average particle diameters (D 50 ), wherein the large particle diameter particles have a lithium composite transition metal oxide in which the content of nickel in the total transition metal is 80 atm% or more , The small particle size particles include nickel, cobalt, and aluminum, the content of nickel in the total transition metal is 80atm% to 85atm%, and the atomic ratio of cobalt to aluminum (Co / Al) is 1.5 to 5 A cathode material that is a lithium composite transition metal oxide. [Claim 2] The cathode material according to claim 1, wherein the small particle size particle is a lithium composite transition metal oxide represented by the following [Formula 1]. [Formula 1] Li x [Ni y Co z Al w M 1 v ]O 2 In Formula 1, M 1 is Mn, W, Cu, Fe, Ba, V, Cr, Ti, Zr, Zn, In, At least one selected from the group consisting of Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 0.9≤x≤1.5, 0.8≤y≤0.85 , 0