Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Abstract

The present invention provides a positive electrode active material comprising a lithium composite transition metal oxide containing nickel, cobalt, manganese, and aluminum, wherein the lithium composite transition metal oxide has a nickel content of 90 mol% or more among the metals other than lithium, and the Al / Ni molar ratio of aluminum to nickel is 0.015 to 0.034, a positive electrode containing the positive electrode active material, and a lithium secondary battery.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2023-0105931 dated August 11, 2023, Korean Patent Application No. 10-2023-0133819 dated October 6, 2023, and Korean Patent Application No. 10-2024-0008351 dated January 18, 2024, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference.

[0002] This invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0003] Recently, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for rechargeable batteries that are small, lightweight, and relatively high-capacity has been rapidly increasing. In particular, lithium-ion batteries are attracting attention as a power source for portable devices due to their light weight and high energy density. As a result, research and development efforts to improve the performance of lithium-ion batteries are being actively pursued.

[0004] Lithium-ion secondary batteries produce electrical energy through oxidation and reduction reactions that occur when lithium ions are inserted into and removed from the positive and negative electrodes, with an organic electrolyte or polymer electrolyte filled between the positive and negative electrodes, which are made of an active material that allows for the insertion and removal of lithium ions.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Furthermore, to maintain the excellent reversible capacity of LiNiO2 and improve its low thermal stability, lithium composite metal oxides (hereinafter simply referred to as "NCM-based lithium composite transition metal oxides") have been developed in which some of the nickel (Ni) is replaced with cobalt (Co) and manganese (Mn). However, conventionally developed NCM-based lithium composite transition metal oxides have not had sufficient capacity characteristics and have had limitations in their application.

[0006] To address these issues, recent research has focused on increasing the nickel content in NCM-based lithium composite transition metal oxides. However, high-nickel (High-Ni) cathode active materials, due to the high reactivity of nickel, generate large amounts of gas during the charge-discharge process. This leads to significant lattice structure instability due to cation mixing and oxygen desorption, resulting in an increased amount of lithium impurities remaining on the surface.

[0007] Therefore, there is a need to develop a cathode material that offers excellent capacity due to its high nickel content, while also ensuring structural stability. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention provides a positive electrode active material with improved dispersibility, a positive electrode slurry containing the same, a positive electrode, and a lithium secondary battery. [Means for solving the problem]

[0009] The present invention relates to a positive electrode active material (NCMA oxide) comprising a lithium composite transition metal oxide containing nickel, cobalt, manganese, and aluminum, The content of nickel among the metals other than lithium in the lithium composite transition metal oxide is 90 mol% or more, and the molar ratio of aluminum to nickel, Al / Ni, is 0.015 to 0.034, providing a positive electrode active material.

[0010] Further, the present invention provides a positive electrode including a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer contains the above-described positive electrode active material.

[0011] Further, the present invention provides a lithium secondary battery including the above-described positive electrode, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

Effects of the Invention

[0012] The positive electrode active material according to the present invention is excellent in capacity because of its high nickel content, and thus the amount of cobalt used can be reduced, which is advantageous in terms of supply and demand and price of materials.

[0013] In addition, in the NCMA oxide, an optimal Al / Ni molar ratio that can uniformly improve the doping yield, resistance characteristics, and structural stability is provided. Thus, since the NCMA oxide is included, a lithium secondary battery with improved charge-discharge capacity and high-temperature life can be provided.

Brief Description of the Drawings

[0014] [Figure 1] It is a graph showing the change in heat flow rate with temperature of a positive electrode active material containing a lithium composite transition metal oxide produced in Examples and Comparative Examples. [Figure 2] It is a graph showing the capacity retention rate and resistance increase rate at high temperature of a half cell containing a lithium composite transition metal oxide produced in Examples and Comparative Examples as a positive electrode active material.

Modes for Carrying Out the Invention

[0015] Hereinafter, the present invention will be specifically described.

[0016] In the present invention, the content of each element in the positive electrode active material can be measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). Specifically, it means that after dispersing and dissolving 0.03 g of the positive electrode active material to be analyzed in 1 mL of hydrochloric acid, adding a small amount of hydrogen peroxide and hydrofluoric acid, diluting with 50 mL of ultrapure water, and then analyzing using an Avio series (PerkinElmer, Inc) instrument.

[0017] In the present invention, the "primary particle" means a particle unit that does not have grain boundaries in appearance when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0018] In the present invention, the "a-axis" and the "c-axis" mean the axial directions in the crystal structure of the primary particle. The crystal structure of the primary particle is confirmed by TEM-SAED (Transmission Electron Microscope-Selected Area Electron diffraction; restricted field electron diffraction) analysis. The length in the c-axis direction and the length in the a-axis direction can be quantitatively analyzed using X-ray diffraction analysis (XRD) with Cu Kα X-rays.

[0019] In the present invention, "X-ray diffraction analysis (XRD)" can be performed by placing the particles to be measured into a holder, irradiating the particles with X-rays, and analyzing the resulting diffraction pattern. Sampling is performed by placing a powder sample of the target particles into the central recessed groove of a general powder holder, leveling the surface using a glass slide, and ensuring the sample height is the same as the edge of the holder. Next, X-ray diffraction analysis is performed using a Bruker D8 Endeavor (light source: Cu Kα, λ=1.54Å) equipped with a LynxEye XE-T position-sensitive detector, in the region of FDS 0.5°, 2θ=15°~90°, with a step size of 0.02° and a total scan time of approximately 20 minutes. Rietveld refinement is then performed on the measured data, taking into account the charge at each site (metal ions at transition metal sites are +3, Ni ions at Li sites are +2) and cation mixing. Instrumental brodending is implemented using the fundamental parameter approach implemented by the Bruker TOPAS program. The Parameter Approach (FPA) is used for fitting, and during fitting, the entire peak of the measurement range is used. The peak shape is FP (First Principle) from the peak types available in TOPAS, and fitting is performed using only the Lorenzian contribution, without considering strain.

[0020] In this invention, "particle strength" is the value expressed in pressure units (MPa) when the powder to be measured is placed in an Anton Paar Step 500 Micro Compression Testing Machine, the shape of the particles to be measured is secured using a microscope, and then force is applied to the particles with a tip until the particles break. Considering the deviation between particles, the values ​​measured 10 or more times are mapped, and the average value is used as the particle strength value.

[0021] In the present invention, "D 50 "50% of the volume cumulative particle size distribution of the particle powder" refers to the particle size corresponding to 50% of the volume cumulative amount, and can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size analyzer (e.g., Malvern Mastersizer 3000), irradiated with ultrasound at approximately 28 kHz with an output of 60 W, and then a volume cumulative particle size distribution graph is obtained. The particle size at the point where the volume cumulative amount is 50% in the obtained volume cumulative particle size distribution graph can then be determined.

[0022] The various components of the present invention will be described in more detail below.

[0023] <Cathode active material> This invention relates to a positive electrode active material, specifically a positive electrode active material for lithium secondary batteries.

[0024] The positive electrode active material according to the present invention comprises a lithium composite transition metal oxide containing nickel, cobalt, manganese, and aluminum. The nickel content among the metals other than lithium in the lithium composite transition metal oxide is 90 mol% or more, and the molar ratio of aluminum to nickel, Al / Ni, is 0.015 to 0.034.

[0025] As mentioned above, while increasing the nickel content in lithium-composite transition metal oxides can ensure high capacity, it also leads to a decrease in structural stability. Specifically, high-nickel cathode active materials have a large amount of lithium compounds remaining on the surface, which can cause side reactions during the charge-discharge process, generating gases and potentially leading to reduced stability.

[0026] Furthermore, high-nickel cathode active materials have the disadvantage of significant changes in the lattice constant, i.e., changes in the volume within the unit cell. Such volume changes can cause cracks to form within the active material particles. These cracks can lead to the formation of voids within the active material, potentially resulting in a decrease in battery performance.

[0027] Furthermore, due to the high nickel content, a significant amount of cation mixing occurs between lithium ions and nickel ions. This hinders the movement of lithium ions during battery operation, leading to increased battery resistance and reduced battery life.

[0028] Therefore, the inventors have solved the above-mentioned problems in an ultra-high nickel cathode active material with a nickel content of 90 mol% or more by adjusting the ratio of nickel to doping elements, specifically, in a lithium composite transition metal oxide (hereinafter referred to as NCMA oxide) containing Ni, Co, Mn, and Al, to an optimal range of molar ratio of Ni to Al. In NCMA oxides with a Ni content of 90 mol% or more, Al can suppress cracking of active material particles by reducing volume changes within the unit cell and prevent degradation by reducing voids. Therefore, the cathode active material according to the present invention can achieve high capacity and exhibit excellent thermal stability and lifetime characteristics. However, since Al cannot contribute to capacity, and excessive amounts of Al may even hinder the development of capacity, it is important to appropriately adjust the Al content relative to Ni.

[0029] Specifically, the Al / Ni molar ratio of aluminum to nickel can be 0.015 or higher, 0.021 or higher, or 0.030 or higher, and can be 0.034 or lower, or 0.032 or lower. If the Al / Ni ratio is less than 0.015, the lifetime characteristics deteriorate due to the rapid volume change within the unit cell caused by the increase in nickel content, structural instability increases, and the main peak temperature, where the heat flow rate is maximum, decreases, making it difficult to achieve the above-mentioned effects. Conversely, if it exceeds 0.034, the excess Al cannot be incorporated into the layered structure and remains on the surface of the active material as undoped residue, hindering the movement of lithium ions, which is undesirable because it increases surface resistance and reduces the expressed capacity.

[0030] In one embodiment of the present invention, the nickel content among the metals other than lithium in the lithium composite transition metal oxide can be 92 mol% or more, preferably 93 mol% or more, and more preferably 93 mol% to 95 mol%. This is preferable in that it can achieve high capacity and ensure an Al content above a predetermined level.

[0031] Furthermore, the cobalt content among the metals other than lithium in the lithium composite transition metal oxide can be 0.1 mol% to 1.0 mol%, preferably 0.2 mol% to 0.9 mol%, and more preferably 0.4 mol% to 0.8 mol%. In other words, the present invention minimizes the content of expensive cobalt and improves lifetime, resistance, and output characteristics by adjusting the Al / Ni molar ratio.

[0032] Furthermore, the aluminum content among the metals other than lithium in the lithium composite transition metal oxide can be 1.0 mol% to 5.0 mol%, preferably 1.5 mol% to 4.0 mol%, and more preferably 2.0 mol% to 3.8 mol%. When the aluminum content is within the above range, it is easy to adjust the Al / Ni molar ratio to the above-mentioned optimal range in an NCMA oxide with a nickel content of 90 mol% or more.

[0033] Specifically, the lithium composite transition metal oxide can have the composition represented by the following Chemical Formula 1.

[0034] [Chemical Formula 1] Li 1+x (Ni a Co b Mn c Al d M1 e )O2

[0035] In Chemical Formula 1, M1 is one or more selected from the group consisting of Ti, Zr, W, Mo, Nb, Cu, Fe, V, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Mg, and B. x, a, b, c, d, and e each satisfy -0.2 ≦ x ≦ 0.2, 0.90 ≦ a < 1, 0 < b ≦ 0.01, 0 < c ≦ 0.05, 0 < d ≦ 0.05, 0 ≦ e ≦ 0.05, and a + b + c + d + e = 1.

[0036] 1 + x represents the molar ratio of lithium in the lithium composite transition metal oxide, and can be -0.1 ≦ x ≦ 0.2 or 0 ≦ x ≦ 0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium composite transition metal oxide can be stably formed.

[0037] a represents the molar ratio of nickel among the total metals other than lithium in the lithium composite transition metal oxide, and can be 0.920 ≦ a < 1, 0.930 ≦ a < 1, or 0.930 ≦ a ≦ 0.950. When the molar ratio of nickel satisfies the above range, it exhibits a high energy density and enables the realization of a high capacity.

[0038] b represents the molar ratio of cobalt among the total metals other than lithium in the lithium composite transition metal oxide, and can be 0 < b ≦ 0.009, 0 < b ≦ 0.008, or 0 < b ≦ 0.006. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized with a minimum amount.

[0039] c represents the molar ratio of manganese among the total metals other than lithium in the lithium composite transition metal oxide, and can be 0 < c ≤ 0.050, 0 < c ≤ 0.040, or 0 < c ≤ 0.030. When the molar ratio of manganese satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0040] d represents the molar ratio of Al among the total metals other than lithium in the lithium composite transition metal oxide, and d can be 0.010 ≤ d ≤ 0.050, 0.015 ≤ d ≤ 0.040, or 0.020 ≤ d ≤ 0.038.

[0041] e represents the molar ratio of the M1 element among the total metals other than lithium in the lithium composite transition metal oxide, and can be adjusted as needed.

[0042] On the other hand, the positive electrode active material includes primary particles and secondary particles formed by aggregation of the primary particles. The ratio c / a of the length in the c-axis direction to the length in the a-axis direction of the primary particles can be 4.9400 - 4.9500, preferably 4.9400 - 4.9450, and more preferably 4.9405 - 4.9422. The inclusion of the c / a ratio within the above range means that the degree of completion of the layered structure of the positive electrode active material is high. Therefore, when the c / a ratio is within the above range, during charge / discharge, the movement of lithium ions is smooth and the volume change is small, which is effective in improving the characteristics of life reduction associated with the progress of the cycle.

[0043] Also, the D 50 of the positive electrode active material can be 8 μm - 15 μm, preferably 10 μm - 13 μm, and more preferably 11 μm - 12 μm. The average particle size of the primary particles can be 0.3 μm - 2.0 μm, preferably 0.5 μm - 1.5 μm, and more preferably 0.7 μm - 1.0 μm, but is not limited thereto.

[0044] On the other hand, because the bond energy between Al and O is greater than the bond energy between Ni and O, adjusting the Al / Ni molar ratio to the above range has the effect of improving the particle strength. For example, the particle strength of the positive electrode active material can be 142 MPa to 160 MPa, preferably 145 MPa to 155 MPa, and more preferably 150 MPa to 155 MPa. When the particle strength is within the above range, cracking of the positive electrode active material is minimized during electrode rolling, and side reactions with the electrolyte are reduced, thereby lowering the rate of increase in battery resistance.

[0045] On the other hand, when the heat flow of the positive electrode active material is measured by differential scanning calorimetry (DSC), the peak where the heat flow is maximum can be between 219°C and 230°C, specifically between 220°C and 230°C, and more specifically between 225°C and 230°C.

[0046] Furthermore, by differential scanning calorimetry (DSC), the maximum heat flow of the positive electrode active material measured in the range of 25°C to 300°C can be 85.0 W / g or less, 70.0 W / g or less, or 60.0 W / g or less.

[0047] In other words, the positive electrode active material according to the present invention has the advantage of having a relatively high peak temperature at which the heat flow rate is maximum, and a small maximum value for the heat flow rate, thus reducing the risk of explosion even when the temperature inside the battery rises.

[0048] On the other hand, the positive electrode active material is subjected to a coprecipitation reaction in a reactor while supplying a transition metal-containing solution containing a transition metal precursor, an ammonium cation complex-forming agent, and a basic compound to form a composite transition metal precursor having a nickel content of 90 mol% or more. It can be produced by a manufacturing method comprising the steps of mixing the composite transition metal precursor, a lithium raw material, and an aluminum raw material, and heat-treating them to form an Al-doped lithium composite transition metal oxide.

[0049] Here, the heat treatment can be carried out at 600°C to 900°C, preferably 650°C to 850°C, and more preferably 700°C to 800°C, for 15 to 24 hours.

[0050] The step of forming the composite transition metal precursor can be carried out, for example, by dissolving each transition metal precursor in a solvent to produce a transition metal-containing solution, then mixing the transition metal-containing solution, an ammonium cation complex-forming agent, and a basic compound, and finally carrying out a coprecipitation reaction. Furthermore, if necessary, an oxidizing agent or oxygen gas may be added during the coprecipitation reaction.

[0051] On the other hand, the transition metal precursor can be an acetate, carbonate, nitrate, sulfate, halide, or sulfide of each transition metal.

[0052] Specifically, the nickel precursor can be one or more selected from the group consisting of NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, and nickel sulfide. The cobalt precursor can be one or more selected from the group consisting of Co(OH)2, Co3SO4, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, and Co(SO4)2·7H2O. The manganese precursor can be one or more selected from the group consisting of Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, and manganese sulfide.

[0053] Here, the amount of each transition metal precursor added can be determined by considering the molar ratio of the transition metal in the cathode active material that is ultimately to be produced.

[0054] On the other hand, the ammonium cation complex-forming agent may contain at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and the compound may be introduced into the reactor in the form of a solution in which it is dissolved in a solvent. Here, the solvent may be water, or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol, etc.).

[0055] The basic compound can be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and the compound can be introduced into the reactor in the form of a solution in which it is dissolved in a solvent. Here, the solvent can be water, or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol, etc.).

[0056] As described above, when the transition metal-containing solution, ammonium cation complex-forming agent, and basic compound are added to the reactor and stirred, the transition metal in the transition metal-containing solution co-precipitates, and precursor particles in the form of transition metal hydroxide are generated.

[0057] Here, the transition metal-containing solution, the ammonium cation complex-forming agent, and the basic compound are added in amounts such that the pH of the reaction solution falls within the desired range.

[0058] Once precursor particles are formed by the method described above, they are separated from the reaction solution to obtain the precursor. For example, the reaction solution can be filtered to separate the precursor, and then the separated precursor can be washed with water and dried to obtain the precursor. Here, if necessary, steps such as grinding and / or classification may be performed.

[0059] The composite transition metal precursor produced in this manner is mixed with a lithium raw material and a precursor containing metal element M1, and then heat-treated to produce a lithium composite transition metal oxide.

[0060] As the lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides can be used. For example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof can be used.

[0061] On the other hand, the lithium raw material and the composite transition metal precursor can be mixed such that the molar ratio of Li to total metal in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1. When the mixing ratio of the lithium raw material and the metal in the precursor satisfies the above range, the layered crystal structure of the lithium composite transition metal oxide develops well, and a positive electrode active material with excellent capacitance characteristics and structural stability can be produced.

[0062] Furthermore, the aluminum raw material can be an Al-containing oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate, or sulfate, 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. The aluminum raw material may be added to the transition metal-containing solution during the coprecipitation reaction instead of being added together with the lithium raw material in the heat treatment step.

[0063] When doping with additional metal element M1, the type and amount of metal element M1 added can be adjusted considering the type and content of metal element M1 contained in the positive electrode active material described above.

[0064] <Positive electrode> Next, the positive electrode according to the present invention will be described.

[0065] The positive electrode according to the present invention includes the positive electrode active material. Specifically, the positive electrode according to the present invention includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material. As the positive electrode active material is as described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0066] The positive electrode current collector is not particularly limited as long as it contains a highly conductive metal, allows for easy adhesion of the positive electrode active material layer, and is unreactive within the battery voltage range. Examples of materials that can be used for the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on its surface to enhance the adhesion of the positive electrode active material. It can be used in various forms, such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0067] The positive electrode can be manufactured by a conventional positive electrode manufacturing method, except for using the positive electrode material described above. Specifically, it can be manufactured by applying a positive electrode slurry containing the positive electrode active material onto a positive electrode current collector, followed by drying and rolling, or by casting the positive electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0068] In one embodiment of the present invention, the positive electrode includes a positive electrode active material layer formed by coating at least one surface of a positive electrode current collector with a positive electrode slurry containing the positive electrode active material.

[0069] On the other hand, the positive electrode slurry may contain the positive electrode active material, binder, conductive material, and solvent.

[0070] Specifically, the binder can be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and is preferably polyvinylidene fluoride.

[0071] The binder can be included in the positive electrode slurry in an amount of 0.5% to 3% by weight, preferably 1% to 3% by weight, and more preferably 1.5% to 2.5% by weight, relative to the total weight of the solids. When the binder content is within this range, sufficient adhesion to the current collector and interparticle bonding are ensured, thereby improving the durability of the positive electrode and maintaining a low initial resistance.

[0072] The conductive material can be one or more selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal 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; and conductive polymers such as polyphenylene derivatives. Preferably, it can be carbon nanotubes or carbon black, and most preferably, carbon nanotubes.

[0073] The conductive material can be included in the positive electrode slurry in an amount of 0.1% to 2.5% by weight, preferably 0.5% to 2% by weight, and more preferably 1% to 2% by weight, relative to the total weight of the solids. When the content of the conductive material is within the above range, it is preferable in that it is possible to maintain conductivity between the active materials and reduce dead volume.

[0074] In addition, the positive electrode slurry may further selectively contain a dispersant, which may be hydrogenated nitrile butadiene rubber (HNBR).

[0075] On the other hand, the solvent of the positive electrode slurry can be a solvent commonly used in the art, such as N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, dimethylformamide (DMF), acetone, water, or a mixture of two or more of these. The solvent can be adjusted to ensure that the positive electrode slurry has an appropriate viscosity. For example, the solvent can be included such that the concentration of solids in the positive electrode slurry is 60% by weight or more, preferably 60% to 90% by weight, and more preferably 60% to 80% by weight.

[0076] Lithium-ion rechargeable battery Next, the lithium secondary battery according to the present invention will be described.

[0077] The lithium secondary battery specifically includes a positive electrode, a negative electrode containing a negative electrode active material, and a separator and electrolyte interposed between the positive electrode and the negative electrode. The positive electrode is as described above, and a detailed explanation will be omitted; only the remaining components will be described in detail below.

[0078] Further, the lithium secondary battery may further selectively include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0079] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0080] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, the negative electrode current collector can usually have a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0081] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0082] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; SiO βExamples include metallic oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more mixtures thereof can be used. A metallic lithium thin film can also be used as the negative electrode active material. The negative electrode active material can be present in an amount of 80% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0083] The binder is a component that helps to bond the conductive material, active material, and current collector, and is usually added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0084] The conductive material is a component for further improving the conductivity of the negative electrode active material and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, relative to the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0085] The negative electrode active material layer can be manufactured by coating a negative electrode composite material, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode composite material onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0086] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0087] Furthermore, the electrolytes 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.

[0088] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0089] The aforementioned organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0090] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt is F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - , (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - The lithium salt can be selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used within the range of 0.1 to 4.0 M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0091] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride. Here, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0092] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, rectangular, pouch-shaped, or coin-shaped, using a can.

[0093] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention exhibit stable charge / discharge capacity and life characteristics, and are therefore not only suitable for use as battery cells in power supplies for small devices such as mobile phones, notebook computers, and digital cameras, but can also be preferably used as unit batteries in battery modules for medium- and large-sized devices that contain a large number of battery cells.

[0094] Examples of the aforementioned medium- and large-sized devices include, but are not limited to, power tools, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0095] 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.

[0096] The present invention will be described in more detail below with reference to specific examples.

[0097] [Example: Production of positive electrode active material] Example 1. Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and then 100 ml of a 28 wt% aqueous ammonia solution was added while maintaining the temperature at 50°C. Next, a transition metal solution prepared by mixing NiSO4, CoSO4, and MnSO4 in a Ni:Co:Mn molar ratio of 97.0:0.5:2.5, an aqueous ammonia solution, and a sodium hydroxide solution were added to the coprecipitation reactor to form a precursor. The precursor particles were separated and washed, and then dried in an oven at 130°C to produce the precursor.

[0098] LiOH as a lithium raw material, the aforementioned manufactured precursor, and Al(OH)3 were mixed so that the molar ratio of Li:(Ni+Co+Mn):Al was 1:0.978:0.022. The mixture was then heat-treated at 720°C for 20 hours under an oxygen atmosphere to produce a lithium composite transition metal oxide.

[0099] Example 2. A precursor was prepared using the same process as in Example 1. LiOH, the prepared precursor, and Al(OH)3 were mixed so that the molar ratio of Li:(Ni+Co+Mn):Al was 1:0.968:0.032, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to produce a lithium composite transition metal oxide.

[0100] Comparative Example 1. A precursor was prepared using the same process as in Example 1. LiOH was mixed with the prepared precursor so that the molar ratio of Li:(Ni+Co+Mn) was 1:1, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to produce a lithium composite transition metal oxide.

[0101] Comparative Example 2. A precursor was prepared using the same process as in Example 1. LiOH, the prepared precursor, and Al(OH)3 were mixed so that the molar ratio of Li:(Ni+Co+Mn):Al was 1:0.989:0.011, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to produce a lithium composite transition metal oxide.

[0102] Comparative Example 3. A precursor was prepared using the same process as in Example 1. LiOH, the prepared precursor, and Al(OH)3 were mixed so that the molar ratio of Li:(Ni+Co+Mn):Al was 1:0.964:0.036, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to produce a lithium composite transition metal oxide.

[0103] Comparative Example 4. Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and then 100 ml of a 28 wt% aqueous ammonia solution was added while maintaining the temperature at 50°C. Next, a transition metal solution prepared by mixing NiSO4, CoSO4, and MnSO4 in a Ni:Co:Mn molar ratio of 91.0:6.0:3.0, an aqueous ammonia solution, and a sodium hydroxide solution were added to the coprecipitation reactor to form a precursor. The precursor particles were separated and washed, and then dried in an oven at 130°C to produce the precursor.

[0104] LiOH as a lithium raw material, the aforementioned manufactured precursor, and Al(OH)3 were mixed so that the molar ratio of Li:(Ni+Co+Mn):Al was 1:0.969:0.031. The mixture was then heat-treated at 720°C for 20 hours under an oxygen atmosphere to produce a lithium composite transition metal oxide.

[0105] [Example of experiment] Experimental Example 1: Confirmation of Doping Content For each of the lithium composite transition metal oxides produced in Examples 1 and 2 and Comparative Examples 1 to 4, the Al content was measured using an inductively coupled plasma atomic emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer). The Al content relative to the total weight and total number of moles of the lithium composite transition metal oxide was calculated and is shown in Table 1 below.

[0106] [Table 1]

[0107] Referring to Table 1, doping was performed in Examples 1 and 2 and Comparative Examples 2-4 with a yield of 93%, and as a result, it can be confirmed that the lithium composite transition metal oxides produced in Examples 1 and 2 ultimately had an Al / Ni molar ratio in the range of 0.015 to 0.034. On the other hand, Comparative Examples 2 and 3 had Al / Ni molar ratios of 0.011 and 0.036, respectively, which deviated from the scope of the present invention, and in the case of Comparative Example 4, where the Ni content was less than 90 mol%, the Al / Ni molar ratio was measured in the same manner as in Example 2.

[0108] Experimental Example 2. XRD Analysis The c / a ratio was measured for each of the lithium composite transition metal oxides produced in Examples 1 and 2 and Comparative Examples 1 and 2 using X-ray diffraction analysis (XRD) with Cu Kα X-rays by the method described above, and the results are as follows.

[0109] [Table 2]

[0110] According to Table 2, the lithium composite transition metal oxides of Examples 1 and 2 had a C / A ratio within the range of 4.9400 to 4.9500, which means that lithium composite transition metal oxides with a higher degree of completeness of the layered structure were produced compared to Comparative Examples 1 and 2, which did not fall within this range.

[0111] Experimental Example 3. Measurement of Particle Intensity Three g each of the lithium composite transition metal oxides produced in Examples 1 and 2 and Comparative Examples 1 and 2 was taken, and the particle strength was measured using a Micro Compression Testing Machine (Shimadzu, MCT-W500) by gradually increasing the pressure and measuring the pressure at which the particles broke. The results are shown in Table 3 below.

[0112] [Table 3]

[0113] From the results in Table 3, it can be confirmed that the lithium composite transition metal oxides produced in Examples 1 and 2 have far superior particle strength compared to the lithium composite transition metal oxides produced in Comparative Examples 1 and 2.

[0114] This effect is achieved because the bond energy between Al and O is even greater than the bond energy between Ni and O. Such high particle strength is advantageous because it mitigates particle cracking during the rolling process.

[0115] Experimental Example 4.D 50 Measurement 0.1 g of the lithium composite transition metal oxide powder produced in Examples 1 and 2 and Comparative Examples 1 to 4 was dispersed in a dispersion medium, then introduced into a laser diffraction particle size analyzer (Malvern, Mastersizer 3000), and ultrasonic waves of approximately 28 kHz were irradiated at an output of 60 W to determine the D of each cathode material powder. 50 The following measurements were taken. The measurement results are shown in Table 4 below.

[0116] [Table 4]

[0117] Experimental Example 5. DSC Evaluation To evaluate the thermal stability of the lithium composite transition metal oxides produced in Examples 1 and 2 and Comparative Examples 1 and 2, the heat flow rate was measured using a differential scanning calorimeter (HP-DSC manufactured by Setaram), and the results are shown in Figure 1 and Table 3 below.

[0118] First, a positive electrode slurry was prepared by mixing the lithium composite transition metal oxides produced in Examples 1 and 2 and Comparative Examples 1 and 2 as positive electrode active materials, carbon black (Denka, Li-435) as a conductive material, PVDF (Kureha, KF9709) as a binder, and acrylate (Zeon, BM-730H) as a dispersant in an NMP solvent in a weight ratio of 95.0:2.0:2.8:0.2. The prepared positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode. An electrode assembly was prepared by interposing a porous polyethylene separator between the prepared positive electrode and the lithium metal negative electrode. This assembly was then placed inside a battery case, and an electrolyte was injected into the case to produce a half cell. The electrolyte was prepared by dissolving 1M LiPF6 in a mixed organic solvent consisting of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 3:4:3.

[0119] The manufactured half-cells were charged at 25°C with a constant current of 0.2C until they reached 4.25V, preparing cells with a state of charge (SOC) of 100%. The fully charged cells were disassembled, the positive electrodes were recovered, and the recovered positive electrodes were washed with DMC for 30 seconds to remove any electrolyte remaining on the surface, after which they were dried. The dried positive electrodes were punched out to match the size of the differential scanning calorimeter pan, placed in the pan with 20 μl of the same electrolyte used in the half-cells, and then the pan was sealed. Next, the heat flow rate was measured while increasing the temperature from 25°C to 300°C at a rate of 10°C per minute, and the results are shown in Figure 1.

[0120] On the other hand, the temperature at which the main peak, where the heat flow rate is maximum, is measured, and the maximum value of the heat flow rate are listed in Table 5 below.

[0121] [Table 5]

[0122] Referring to Table 5 and Figure 1, when using the lithium composite transition metal oxides of Examples 1 and 2, in which the Al / Ni molar ratio is in the range of 0.015 to 0.034, as the positive electrode active material, the main peak where the heat flow is maximum is high, and the maximum value of the heat flow is low. Therefore, it can be confirmed that even when the temperature inside the battery rises, the risk of explosion is relatively low.

[0123] In particular, in Example 2, the maximum heat flow rate is 60 W / g or less, and the main peak temperature is 220°C or higher, demonstrating the best thermal stability.

[0124] Experimental Example 6. Capacity and Lifetime Evaluation (1) Manufacturing of half cells A cathode containing the lithium composite transition metal oxide produced in the examples and comparative examples, as well as a half-cell containing the same, was manufactured using the same method as in Experimental Example 5.

[0125] (2) Measurement of initial capacity and efficiency After performing an activation process on each half-cell manufactured in (1) above, the cells were charged to 4.25V at 25°C and 0.2C (reference capacity 1C = 200mAh / g) using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd.) under CC-CV conditions, and then discharged to 2.5V at 0.2C under CC conditions. The initial charge / discharge capacity and initial efficiency were measured and recorded in Table 6 below.

[0126] (3) Evaluation of high-temperature life Each half-cell manufactured in (1) above underwent an activation (formation) process, and was then charged to 4.25V at 45°C and 0.33C (reference capacity 1C = 200mAh / g) under CC-CV conditions using a PNE-0506 charge / discharger (manufacturer: PNE Solutions Co., Ltd.), and discharged to 2.5V at 0.33C under CC conditions. This charge / discharge was considered one cycle, and after one cycle, the initial discharge capacity and initial resistance were measured. Then, the same charge / discharge was repeated for up to 30 cycles, and the capacity and resistance values ​​were measured. Based on this, the capacity retention rate relative to the initial discharge capacity and the resistance increase rate relative to the initial resistance were calculated, and the results are shown in Figure 2 and Table 6.

[0127] [Table 6]

[0128] Referring to Table 6 above, it can be confirmed that the cells of Examples 1 and 2, which use a lithium composite transition metal oxide with an Al / Ni molar ratio in the range of 0.015 to 0.034 as the positive electrode active material, all have an initial charge / discharge efficiency of 88% or higher, a high-temperature capacity retention rate of 93% or higher, and a high-temperature resistance increase rate of 92% or less.

[0129] On the other hand, in Comparative Examples 1 and 2, where lithium composite transition metal oxides were used as the positive electrode active material, either without Al or with an Al / Ni molar ratio of 0.011, it was confirmed that the high-temperature capacity retention rate and high-temperature resistance increase rate were significantly reduced. In particular, it was confirmed that the high-temperature resistance increase rate was very high, exceeding 110%.

[0130] Furthermore, it can be confirmed that the cell of Comparative Example 3, which uses a lithium composite transition metal oxide with an Al / Ni molar ratio of 0.036 as the positive electrode active material, has low initial capacity and efficiency, and a high rate of increase in high-temperature resistance.

[0131] Furthermore, the positive electrode active material used in Comparative Example 4 has the same Al / Ni molar ratio as the positive electrode active material used in Example 2, but differs in that its nickel content is less than 90 mol%. As a result, it can be confirmed that the initial charge / discharge capacity itself is lower, and the resistance increase rate at high temperatures is significantly increased.

Claims

1. A positive electrode active material comprising a lithium composite transition metal oxide containing nickel, cobalt, manganese, and aluminum, The positive electrode active material wherein the nickel content among the metals other than lithium in the lithium composite transition metal oxide is 90 mol% or more, and the Al / Ni molar ratio of aluminum to nickel is 0.015 or more and 0.034 or less.

2. The positive electrode active material according to claim 1, wherein the Al / Ni ratio is 0.021 or more and 0.032 or less.

3. The positive electrode active material according to claim 1, wherein the nickel content among the metals other than lithium in the lithium composite transition metal oxide is 93 mol% to 95 mol%.

4. The positive electrode active material according to claim 1, wherein the cobalt content among the metals other than lithium in the lithium composite transition metal oxide is 0.1 mol% to 1.0 mol%.

5. The positive electrode active material according to claim 1, wherein the aluminum content among the metals other than lithium in the lithium composite transition metal oxide is 1.0 mol% to 5.0 mol%.

6. The lithium composite transition metal oxide has the composition of the following chemical formula 1, [Chemical formula 1] Li １＋ｘ (N ａ Co ｂ Mn ｃ Al ｄ M1 ｅ )O ２ In the aforementioned chemical formula 1, M1 is one or more elements selected from the group consisting of Ti, Zr, W, Mo, Nb, Cu, Fe, V, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Mg, and B. The positive electrode active material according to claim 1, wherein x, a, b, c, d, and e satisfy -0.2 ≤ x ≤ 0.2, 0.90 ≤ a < 1, 0 < b ≤ 0.01, 0 < c ≤ 0.05, 0 < d ≤ 0.05, 0 ≤ e ≤ 0.05, and a + b + c + d + e = 1, respectively.

7. The positive electrode active material includes primary particles and secondary particles formed by aggregation of the primary particles. The positive electrode active material according to claim 1, wherein the ratio c / a, which is the ratio of the length in the c-axis direction to the length in the a-axis direction of the primary particle, is 4.9400 to 4.9500.

8. The positive electrode active material according to claim 1, wherein the particle strength of the positive electrode active material is 142 MPa to 160 MPa.

9. The positive electrode active material according to claim 1, wherein when the heat flow of the positive electrode active material is measured by differential scanning calorimetry (DSC), the peak where the heat flow is maximum appears at 219°C to 230°C.

10. The positive electrode active material according to claim 1, wherein the maximum value of the heat flow of the positive electrode active material measured in the range of 25°C to 300°C by differential scanning calorimetry (DSC) is 85.0 W / g or less.

11. Positive electrode current collector and The positive electrode current collector includes a positive electrode active material layer provided on at least one surface of the positive electrode current collector, The positive electrode comprises the positive electrode active material layer described in claim 1.

12. The positive electrode according to claim 11, A negative electrode containing a negative electrode active material, A separator interposed between the positive electrode and the negative electrode, A lithium secondary battery containing an electrolyte.

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