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

Abstract

The positive electrode active material according to the present invention is a positive electrode active material comprising a lithium nickel-based oxide which is a single particle consisting of one single nodule, a quasi-single particle which is a complex of 30 or less nodules, or a combination thereof, and the positive electrode active material is D 90 is 8.0 μm to 11.5 μm, and the negative skewness factor (NSF) represented by the following formula 1 is 0.20 to 0.35, [Formula 1] NSF=(D 50 -D 10 ) / I max In the formula 1, D 50 is the particle size at the point where the cumulative volume is 50% in the volume cumulative particle size distribution graph of the positive electrode active material, and D 10 is the particle size at the point where the cumulative distribution is 10% in the volume cumulative particle size distribution graph of the positive electrode active material, and I max is the maximum volume fraction in the volume cumulative particle size distribution graph of the positive electrode active material.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application Nos. 10-2022-0166990 and 10-2022-0166991, filed December 2, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

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

[0003] With the technological development and increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Lithium transition metal composite oxides are used as the positive electrode active material for lithium secondary batteries, and in particular, lithium nickel-based oxides, which can easily be used to realize high-capacity batteries, have been the subject of active research and development. However, the morphology of secondary particles has been problematic in that they can worsen the formation of cracks in the positive electrode active material during charging and discharging.

[0005] To solve the above problems, a technique has been proposed in which a positive electrode active material is produced in the form of a single particle, rather than a secondary particle, by increasing the firing temperature during the production of a lithium nickel-based oxide.

[0006] However, single-particle cathode active materials have problems such as fewer interparticle interfaces, which serve as paths for lithium ions to move, and longer lithium diffusion paths within the particles, resulting in high resistance and poor output. Therefore, conventionally, the average particle size of the particles has been set to 5.0 μm or less to minimize the increase in resistance and decrease in output of single-particle cathode active materials.

[0007] However, in order to reduce the average particle size of the single-particle cathode active material to 5.0 μm or less, a pulverization process with high crushing strength is required. However, this process generates a large amount of fine powder, which causes a rapid decrease in the phase stability of the slurry. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a positive electrode active material having excellent slurry phase stability and electrochemical properties by optimizing the particle size distribution of the positive electrode active material, and a positive electrode slurry, positive electrode, and lithium secondary battery containing the same. [Means for solving the problem]

[0009] In one aspect, the present invention provides a positive electrode active material comprising a lithium nickel-based oxide that is a single particle consisting of one single nodule, a quasi-single particle that is a complex of 30 or less nodules, or a combination thereof, wherein the positive electrode active material is D 90 The positive electrode active material has a particle size of 8.0 μm to 11.5 μm and a negative skewness factor (NSF) represented by the following formula 1 of 0.20 to 0.35.

[0010] [Formula 1] NSF=(D 50 -D 10 ) / I max In the formula 1, D 50 is the particle size at the point where the cumulative volume is 50% in the volume cumulative particle size distribution graph of the positive electrode active material, and D 10 is the particle size at the point where the cumulative distribution is 10% in the volume cumulative particle size distribution graph of the positive electrode active material, and I max is the maximum volume fraction in the volume cumulative particle size distribution graph of the positive electrode active material.

[0011] The positive electrode active material is D 50The thickness can be 5.0 μm to 7.0 μm.

[0012] The positive electrode active material is D 10 can be 2.5 μm to 3.1 μm.

[0013] The lithium nickel-based oxide may be represented by the following Chemical Formula 1:

[0014] [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O2 In the above Chemical Formula 1, M 1 is Mn, Al or a combination thereof, and M 2 is one or more elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and 0≦x≦0.50, 0.80≦a<1.00, 0 <b<0.20、0<c<0.20、および0≦d≦0.20であることができる。

[0015] In the above chemical formula 1, 0.83≦a<1.00, 0 <b<0.17、0<c<0.17、および0≦d≦0.17であることができる。

[0016] The positive electrode active material may have a tap density of 2.32 g / cc or more.

[0017] In another aspect, the present invention provides a positive electrode slurry including the above-described positive electrode active material.

[0018] The positive electrode slurry may have a solid content of 65% to 75% by weight.

[0019] The positive electrode slurry may have a viscosity of 2,000 cp to 5,000 cp measured at 40° C. and a shear rate of 16 rpm.

[0020] In still another aspect, the present invention provides a positive electrode and a lithium secondary battery comprising the above-described positive electrode active material.

[0021] The lithium secondary battery may have a capacity retention rate of 88% or more after 50 charge / discharge cycles, where one cycle is charging at 0.5 C to 4.25 V at 45° C. and discharging at 1.0 C to 3.0 V. [Effects of the Invention]

[0022] The positive electrode active material according to the present invention is NSF and D 90 When the ratio satisfies a specific range, the spaces between the relatively large particles can be filled with small particles to increase the tap density, and the slurry has low viscosity and excellent phase stability, thereby achieving excellent processability.

[0023] Furthermore, the positive electrode active material according to the present invention includes single particles and / or quasi-single particles having excellent particle strength, and thus has less particle cracking during rolling, thereby achieving excellent life characteristics.

[0024] Furthermore, when the particle size distribution according to the present invention is satisfied, the resistance increase rate is low and excellent output performance can be achieved despite the single particle and / or pseudo-single particle morphology. DETAILED DESCRIPTION OF THE INVENTION

[0025] The terms and words used in this specification and claims should not be interpreted in a limited way to their general or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their inventions.

[0026] In the present invention, a "single particle" refers to a particle consisting of one single nodule. In the present invention, a "quasi-single particle" refers to a particle that is a complex formed by 30 or fewer nodules.

[0027] In the present invention, the term "nodule" refers to a particle unit body comprising a single particle or a quasi-single particle, and the nodule may be a single crystal lacking a crystalline grain boundary, or a polycrystal lacking any apparent grain boundary when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope (SEM). The average particle size of the nodules may be measured as the arithmetic mean value of the particle sizes of the respective nodules measured using a scanning electron microscope (SEM).

[0028] In the present invention, the term "secondary particles" refers to particles formed by agglomeration of several tens to several hundreds of primary particles. More specifically, secondary particles are agglomerations of 40 or more primary particles.

[0029] The term "particle" as used in the present invention may include any one or all of single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0030] In the present invention, "D 10 "," "D 50 " and "D 90 " means particle sizes at 10%, 50% and 90% of the volume cumulative particle size distribution of the positive electrode active material. 10 , D 50 and D 90 can be measured using the laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000). After irradiating the dispersion with ultrasonic waves of approximately 28 kHz at an output of 60 W, a volume cumulative particle size distribution graph is obtained, and the particle sizes corresponding to 10%, 50%, and 90% of the volume cumulative amount are determined.

[0031] The present invention will be described in more detail below.

[0032] positive electrode active material The positive electrode active material according to the present invention includes a single particle consisting of one single nodule, a quasi-single particle which is a composite of 30 or less nodules, or a combination thereof.

[0033] Lithium nickel-based oxides in the form of single particles and / or quasi-single particles have higher particle strength than existing lithium nickel-based oxides in the form of secondary particles, which are composed of agglomerates of tens to hundreds of primary particles, and therefore suffer less particle cracking during rolling.

[0034] In addition, in the case of the lithium nickel-based oxide in the form of a single particle or quasi-single particle according to the present invention, the number of lower-component elements (i.e., nodules) constituting the particle is small, so there is little change due to volume expansion and contraction of the primary particles during charge and discharge, and therefore the occurrence of cracks inside the particles is significantly reduced.

[0035] In particular, the inventors of the present invention have developed a Negative Skewness Factor (NSF) and a D 90 When a cathode active material that satisfies a specific range is used, the phase stability of the slurry can be improved by optimizing the particle size distribution. This minimizes particle cracking during the electrode manufacturing process, reducing gas generation. It also minimizes changes in the crystal structure during charging and discharging, reducing the diffusion distance of lithium ions within the particles, achieving low initial resistance characteristics, and maximizing tap density, thereby improving energy density.

[0036] The positive electrode active material according to the present invention is D 90 can be 8.0 μm to 11.5 μm, 9.0 μm to 11.0 μm, or 9.5 μm to 10.5 μm.

[0037] Furthermore, the positive electrode active material according to the present invention may have an NSF value of 0.20 to 0.35, 0.21 to 0.35, or 0.21 to 0.34.

[0038] According to the research of the present inventors,90 When both the D and NSF values ​​are within the above ranges, it is recognized that the viscosity of the slurry is generally low and the tap density is high due to the enlargement of the medium particles and the optimization of the particle size distribution. 90 If neither the D value nor the NSF value meets the above range, it is recognized that the slurry has a high viscosity and a low tap density due to the problem of existing small particles. 90 Alternatively, when only one of the NSF values ​​satisfies the above range, the viscosity of the slurry is low, but the particle size distribution cannot be optimized, and the tap density is reduced.

[0039] Specifically, the positive electrode active material D 90 If the particle size is less than 8.0 μm, the specific gravity of the fine particles will increase, which may reduce the phase stability of the slurry. If the particle size is more than 11.5 μm, the distribution of large particles and particles with a low degree of monoparticulation may increase.

[0040] On the other hand, the positive electrode active material according to the present invention is D 50 can be 5.0 μm to 7.0 μm, 5.5 μm to 6.5 μm, 5.4 μm to 6.5 μm, or 5.6 μm to 6.2 μm.

[0041] The single particle type positive electrode active material that has been commercially available so far is D 50 Generally, the thickness of the pores is 5.0 μm or less. 50 If the size is small, a crushing process with a high crushing strength is required, and in this process, a large amount of fine powder is generated, which causes a rapid decrease in the phase stability of the slurry. 50 By forming the crushing holes relatively large, the crushing process can be carried out with a relatively low crushing pressure, thereby reducing the amount of fine powder generated in the crushing process.

[0042] Specifically, D 50If the particle size is less than 5.0 μm, the amount of fine powder generated increases and the phase stability of the slurry may decrease, and if the particle size exceeds 7.0 μm, the lithium diffusion path within the particle may become long and the resistance and output performance may decrease.

[0043] On the other hand, the positive electrode active material according to the present invention is D 10 can be 2.5 μm to 3.1 μm, 2.6 μm to 3.1 μm, or 2.7 μm to 3.1 μm. 10 If the particle size is less than 2.5 μm or more than 3.1 μm, the effect of improving the phase stability of the slurry may be minimal.

[0044] Meanwhile, the positive electrode active material according to the present invention may include a lithium nickel-based oxide having a composition represented by the following Chemical Formula 1:

[0045] [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O2 In the above Chemical Formula 1, M 1 is Mn, Al or a combination thereof, and M 2 is one or more elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and 0≦x≦0.50, 0.80≦a<1.00, 0 <b<0.20、0<c<0.20、および0≦d≦0.20であることができる。

[0046] The 1+x represents the molar ratio of lithium in the lithium nickel-based oxide, and may be 0≦x≦0.50, 0≦x≦0.30, or 0≦x≦0.20.

[0047] The a represents the molar ratio of nickel to all metals other than lithium in the lithium nickel-based oxide, and may be 0.80≦a<1.00, 0.83≦a<1.00, or 0.86≦a<1.00.

[0048] The b represents the molar ratio of cobalt to all metals other than lithium in the lithium nickel-based oxide, and is 0 <b<0.20、0<b<0.17、または0<b<0.15であることができる。

[0049] The c is M among all metals other than lithium in the lithium nickel-based oxide. 1 indicates the molar ratio of 0 <c<0.20、0<c<0.17、または0<c<0.15であることができる。

[0050] The d is M among all metals other than lithium in the lithium nickel-based oxide. 2 It indicates the molar ratio of the elements and can be 0≦d≦0.20, 0≦d≦0.17, or 0≦d≦0.15.

[0051] The positive electrode active material according to the present invention may have a tap density of 2.32 g / cc or more, 2.40 g / cc or more, or 2.43 g / cc or more. When the tap density of the positive electrode active material according to the present invention satisfies this range, the amount of fine powder is reduced, the phase stability of the slurry is improved, and excellent electrochemical properties can be achieved.

[0052] The cathode active material of the present invention may be prepared by mixing a cathode active material precursor and a lithium source material and then calcining the mixture.

[0053] Here, the positive electrode active material precursor may be a commercially available positive electrode active material precursor, or may be prepared by a precursor preparation method well known in the art.

[0054] For example, the precursor can be prepared by adding an aqueous solution of a transition metal and an ammonium cation complex to a reactor, and then co-precipitation with stirring the resulting mixture.

[0055] The transition metal aqueous solution may be prepared by dissolving a transition metal-containing source material in a solvent such as water, for example, by dissolving a nickel-containing source material, a cobalt-containing source material, or a manganese-containing source material in water. If necessary, the transition metal aqueous solution may further include an aluminum-containing source material.

[0056] Meanwhile, the transition metal-containing raw material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of the transition metal.

[0057] Specifically, the nickel-containing source material may be, for example, NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or combinations thereof.

[0058] The cobalt-containing source material can be, for example, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0059] The manganese-containing source material can be, for example, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, or a combination thereof.

[0060] The aluminum-containing source material 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 be added together with the lithium source material in the calcination step described below, without being added to the transition metal aqueous solution.

[0061] The ammonium cation complexing agent may include at least one compound selected from the group consisting of NHOH, (NH)SO, NHNO, NHCl, CHCOONH, and (NH)CO, and may be added to the reactor in the form of a solution in which the compound is dissolved in a solvent, which may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0062] The basic compound may be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may be added to the reactor in the form of a solution in which the compound is dissolved in a solvent, which may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0063] As described above, when the aqueous transition metal solution, the ammonium cation complexing agent, and the basic compound are charged into a reactor and stirred, the transition metal in the aqueous transition metal solution is coprecipitated to produce precursor particles in the form of transition metal hydroxide.

[0064] Here, the aqueous transition metal 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 a desired range.

[0065] After the precursor particles are formed by the above method, the positive electrode active material precursor is separated from the reaction solution to obtain the positive electrode active material precursor. For example, the reaction solution is filtered to separate the positive electrode active material precursor from the reaction solution, and the separated positive electrode active material precursor is then washed with water and dried to obtain the positive electrode active material precursor. Here, if necessary, steps such as pulverization and / or classification can be performed.

[0066] Next, the positive electrode active material precursor and a lithium raw material are mixed and then calcined to prepare a lithium nickel-based oxide. 1The metal-containing raw materials can be mixed together and fired.

[0067] The lithium source material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, such as Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a mixture thereof.

[0068] Meanwhile, the lithium source material and the cathode active material precursor may be mixed so that the molar ratio of Li:total metals in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1. When the mixing ratio of the lithium source material and the metals in the cathode active material precursor satisfies this range, the layered crystal structure of the cathode active material is well developed, and a cathode material with excellent capacity characteristics and structural stability can be produced.

[0069] Meanwhile, the calcination is carried out under conditions that allow the grains of the positive electrode active material to grow so that the particle size distribution range of the present invention is satisfied.

[0070] The appropriate calcination temperature may vary depending on the composition of the metal in the precursor; for example, if the nickel (Ni) content is 86 mol% or more, the calcination temperature may be 700°C to 1000°C, 800°C to 900°C, or 820°C to 880°C.

[0071] The calcination can be carried out in an air or oxygen atmosphere for 1 to 15 hours, 6 to 15 hours, or 10 to 15 hours. In this specification, an oxygen atmosphere refers to an atmosphere containing sufficient oxygen for calcination, including an air atmosphere. In particular, it is preferable to carry out the calcination in an atmosphere having an oxygen partial pressure higher than that of the air atmosphere.

[0072] After the calcination, a pulverization process is preferably performed to control the particle size distribution to a desired value. Here, the pulverization may be performed using a common pulverization method known in the art, such as a ball mill or a jet mill. When such a pulverization process is performed, the particle size of the positive electrode active material can be more appropriately controlled.

[0073] The grinding can be carried out at a pressure range of 2.0 bar to 4.0 bar, 2.2 bar to 3.8 bar, or 2.4 bar to 3.5 bar.

[0074] The grinding can be carried out at a speed ranging from 1000 rpm to 3000 rpm, from 1200 rpm to 2800 rpm, or from 1300 rpm to 2500 rpm.

[0075] The positive electrode active material produced by the above pressure range and speed range is D 10 , D 50 , and / or D 90 can be appropriately controlled to satisfy a predetermined range, thereby realizing excellent phase stability and electrochemical properties of the slurry.

[0076] Positive electrode slurry Next, the positive electrode slurry according to the present invention will be described.

[0077] The positive electrode slurry according to the present invention includes the positive electrode active material according to the present invention. The positive electrode slurry according to the present invention may optionally include a conductive material and a binder along with the positive electrode active material. Specifically, the positive electrode slurry may be prepared by mixing the positive electrode active material, the conductive material, and / or the binder in a solvent.

[0078] Here, the positive electrode active material may be included in an amount of 80 wt % to 99 wt %, or 90 wt % to 98 wt %, based on the total solid content of the positive electrode slurry.

[0079] The conductive material is used to impart conductivity to the electrode and can be any material that does not cause chemical changes in the resulting battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or 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 powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. The conductive material may be included in an amount of 0.01 wt % to 10 wt %, 0.1 wt % to 9 wt %, or 0.1 wt % to 5 wt % based on the total solids content of the positive electrode slurry.

[0080] The binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, based on the total solid content of the positive electrode slurry.

[0081] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent application for manufacturing a positive electrode, taking into consideration the coating thickness of the positive electrode slurry and manufacturing yield.

[0082] The positive electrode slurry according to the present invention may have a solids content of 65% to 75% by weight, 67% to 74% by weight, or 69% to 72% by weight.

[0083] The positive electrode slurry according to the present invention may have a viscosity of 2,000 cp to 5,000 cp, 2,400 cp to 4,000 cp, or 2,400 cp to 3,500 cp, measured at 40° C. and a shear rate of 16 rpm.

[0084] positive electrode Next, the positive electrode according to the present invention will be described.

[0085] The cathode according to the present invention includes a cathode active material layer including the cathode active material according to the present invention. For example, the cathode may include a cathode active material layer formed using the cathode slurry according to the present invention. Since the cathode active material and the cathode slurry have been described above, detailed descriptions thereof will be omitted and only the remaining components will be described in detail below.

[0086] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to the positive electrode active material layer and is non-reactive within the battery voltage range. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, heat-treated carbon, and aluminum or stainless steel whose surfaces are surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0087] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the above-described positive electrode active material. Specifically, the positive electrode can be manufactured by applying the positive electrode slurry onto a positive electrode current collector, followed by drying and rolling.

[0088] Alternatively, the positive electrode can be produced by casting the positive electrode slurry on a separate support, peeling it off from the support, and laminating the resulting film onto a positive electrode current collector.

[0089] Lithium secondary battery Next, the lithium secondary battery according to the present invention will be described.

[0090] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is as described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0091] The lithium secondary battery may 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.

[0092] 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.

[0093] The negative electrode current collector may be any material that does not cause chemical changes in the battery and has high conductivity, and examples of such materials include copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the current collector may have fine irregularities on its surface to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0094] The negative electrode active material layer may optionally contain a binder and a conductive material in addition to the negative electrode active material.

[0095] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can 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 alloys, Sn alloys or Al alloys; SiO x (0 < x < 2), metal oxides such as SnO2, vanadium oxides, and lithium vanadium oxides that can be doped and undoped with lithium; or composites containing the metallic compound and the carbonaceous material such as Si-C composites or Sn-C composites, etc. Any one or a mixture of two or more of these can be used. Also, a thin film of metallic lithium can be used as the negative electrode active material. Also, as the carbon material, both low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, scaly, spherical or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature heat-treated carbons such as petroleum or coal tar pitch derived cokes.

[0096] The negative electrode active material can be contained in an amount of 80% to 99% by weight, 82% to 99% by weight, or 84% to 99% by weight based on the total weight of the negative electrode active material layer.

[0097] The binder is a component that helps bind the conductive material, active material, and current collector together, and is typically added in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0098] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be included in an amount of 1 wt % to 30 wt %, 1 wt % to 20 wt %, or 1 wt % to 10 wt % based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powder 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.

[0099] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and the resulting film may be laminated on the negative electrode current collector.

[0100] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in lithium secondary batteries can be used without particular limitations. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte humidification capacity are preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, separators coated with ceramic components or polymeric materials can also be used, and they can be selectively used in single-layer or multi-layer structures.

[0101] Furthermore, examples of the electrolyte used in the present invention include 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 production of lithium secondary batteries, but are not limited to these.

[0102] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0103] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0104] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the anion of the lithium salt can be 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 may be at least one selected from the group consisting of: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, 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 a range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0105] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcohol amine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, for the purposes of improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. Here, the additives may be contained in an amount of 0.1 wt % to 10.0 wt % based on the total weight of the electrolyte.

[0106] As described above, the lithium secondary battery including the positive electrode active material according to the present invention may have a capacity retention rate of 88% or more, 88.8% or more, or 88.8% to 99% after 50 charge-discharge cycles, where one cycle is charging at 0.5 C at 45° C. to 4.25 V and discharging at 1.0 C to 3.0 V.

[0107] As described above, the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0108] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0109] The battery module or battery pack may 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 an electric vehicle (PHEV), including a plug-in hybrid electric vehicle; or a power storage system.

[0110] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms without departing from the spirit or scope of the present invention.

[0111] Examples and Comparative Examples Example 1 Positive electrode active material precursor Ni 0.90 Co 0.06 Mn 0.04 (OH)2 and the lithium source material LiOH were mixed in a molar ratio of 1:1, and then the mixture was fired at 810°C for 12 hours.

[0112] Thereafter, the fired product was pulverized under conditions of 2.5 bar and 1400 rpm for 1 hour to obtain the positive electrode active material LiNi 0.90 Co 0.06 Mn 0.04 Produced O2.

[0113] Example 2 The mixture was calcined at 815° C. for 12 hours, and the calcined product was pulverized at 2.5 bar and 1800 rpm for 1 hour, to prepare a positive electrode active material in the same manner as in Example 1.

[0114] Example 3 The mixture was calcined at 810° C. for 15 hours, and the calcined product was pulverized at 2.5 bar and 2400 rpm for 1 hour, to prepare a positive electrode active material in the same manner as in Example 1.

[0115] Comparative Example 1 A positive electrode active material was prepared in the same manner as in Example 1, except that the mixture was calcined at 830° C. for 6 hours and the calcined product was pulverized at 3.0 bar and 800 rpm for 1 hour.

[0116] Comparative Example 2 A positive electrode active material was prepared in the same manner as in Example 1, except that the mixture was calcined at 840° C. for 6 hours and the calcined product was pulverized at 3.0 bar and 800 rpm for 1 hour.

[0117] Comparative Example 3 The mixture was calcined at 750° C. for 12 hours, and the calcined product was pulverized at 2.0 bar and 1600 rpm for 1 hour, to prepare a positive electrode active material in the same manner as in Example 1.

[0118] Comparative Example 4 The mixture was calcined at 810° C. for 12 hours, and the calcined product was pulverized at 2.5 bar and 800 rpm for 1 hour, to prepare a positive electrode active material in the same manner as in Example 1.

[0119] Experimental Example 1: Particle size distribution of positive electrode active material 0.005 g of each of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was dispersed in a dispersion medium HO, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000). Ultrasonic waves of about 28 kHz were irradiated at an output of 60 W to obtain a volume cumulative particle size distribution graph for each positive electrode active material. Using the graph, 90 , D 50 , D 10 The NSF value was calculated using the following formula 1.

[0120] [Formula 1] NSF=(D 50 -D 10 ) / I max In the formula 1, D 50 is the particle size at the point where the cumulative volume is 50% in the volume cumulative particle size distribution graph of the positive electrode active material, and D10 is the particle size at the point where the cumulative distribution is 10% in the volume cumulative particle size distribution graph of the positive electrode active material, and I max is the maximum volume fraction in the volume cumulative particle size distribution graph of the positive electrode active material.

[0121] The results are shown in Table 1 below.

[0122] [Table 1]

[0123] Experimental Example 2: Tap density of positive electrode active material The tap densities of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were measured using a tap density tester (Micromeritics GeoPyc 1365).

[0124] Specifically, 10 g of the positive electrode active material produced in each of Examples 1 to 3 and Comparative Examples 1 to 4 was filled into a 45 cc container, and the container was vibrated horizontally until a force of 108 N was applied, thereby measuring the tap density. The measurement results are shown in Table 2 below.

[0125] [Table 2]

[0126] It can be seen from Table 2 above that the positive electrode active materials of Examples 1 to 3 have higher tap densities than the positive electrode active materials of Comparative Examples 1 to 4.

[0127] Experimental Example 3: Viscosity of Positive Electrode Slurry <Method for producing positive electrode slurry> The positive electrode active materials, carbon black conductive material, and PVDF binder prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were mixed in a weight ratio of 97.0:1.5:1.5 in N-methylpyrrolidone (NMP) to prepare positive electrode slurries with a solid content of 71 wt %.

[0128] The viscosity of the positive electrode slurry was measured using a viscometer (BROOKFIFLD DV2TLVTJ0). Specifically, the positive electrode slurry was filled into a brown 10 ml vial, and the viscosity was measured at 40°C using a No. 25 spindle at a shear rate of 16 rpm. The measurement results are shown in Table 3.

[0129] [Table 3]

[0130] According to the above [Table 3], D falling within the scope of the claims 90 The positive electrode slurries containing the positive electrode active materials prepared in Examples 1 to 3 having the above NSF values ​​are D 90 It can be seen that the viscosity of the positive electrode slurries prepared in Comparative Examples 1 and 2 is lower than that of the positive electrode slurries containing the positive electrode active materials prepared in Comparative Examples 1 and 2, both of which do not satisfy the claimed range in terms of NSF and D. 90 Comparative Example 3, which is not included in the scope of the claims, and D 90 Although the NSF value is within the scope of the claims, the positive electrode slurry containing the positive electrode active material prepared in Comparative Example 4, whose NSF value is outside the scope of the claims, not only has a relatively low tap density as shown in Experimental Example 2, but also exhibits a very high rate of increase in the resistance of the lithium secondary battery as will be described later in Experimental Example 4.

[0131] Experimental Example 4: Electrochemical characteristics of lithium secondary batteries The capacity retention rate (%) and resistance increase rate (%) of the lithium secondary battery coin half-cells prepared as follows using the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were measured. The measurement results are shown in Table 4.

[0132] Specifically, the lithium secondary battery coin half-cell was manufactured as follows.

[0133] Each of the positive electrode slurries prepared in Experimental Example 3 was applied to one side of an aluminum current collector, dried at 130° C., and then rolled to prepare a positive electrode.

[0134] The negative electrode used was lithium metal.

[0135] An electrode assembly was fabricated by interposing a separator between the positive and negative electrodes, and then placed inside a battery case. An electrolyte solution was then injected into the case to fabricate a battery cell. The electrolyte solution was prepared by dissolving 1M LiPF6 in a mixed organic solvent of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) in a volume ratio of 1:1:1, and adding 5 wt% vinylene carbonate (VC).

[0136] For the lithium secondary battery coin half-cells containing the positive electrode active materials produced in Examples 1 to 3 and Comparative Examples 1 to 4, one cycle was defined as charging and discharging at 3.0 V to 4.25 V under conditions of 0.5 C / 1.0 C at 45° C., and the capacity retention rate (%) and resistance increase rate (%) at the 50th cycle were measured.

[0137] [Table 4]

Claims

1. A positive electrode active material comprising a lithium nickel-based oxide that is a single particle consisting of one single nodule, a quasi-single particle that is a composite of 30 or less nodules, or a combination thereof, The positive electrode active material is D ９０ is 8.0 μm to 11.5 μm, The negative skewness factor (NSF) represented by the following formula 1 is 0.20 to 0.35, [Formula 1] NSF=(D ５０ -D １０ ) / I ｍａｘ In the formula 1, D ５０ is the particle size at the point where the cumulative volume is 50% in the volume cumulative particle size distribution graph of the positive electrode active material, and D １０ is the particle size at a point where the cumulative distribution is 10% in the volume cumulative particle size distribution graph of the positive electrode active material, and I ｍａｘ is the maximum volume fraction in a volume cumulative particle size distribution graph of the positive electrode active material.

2. The positive electrode active material has a D of 5.0 μm to 7.0 μm. ５０ The positive electrode active material according to claim 1 , having

3. The positive electrode active material has a D of 2.5 μm to 3.1 μm. １０ The positive electrode active material according to claim 1 , having

4. The lithium nickel-based oxide is represented by the following chemical formula 1: [Chemical formula 1] Li １＋ｘ Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２ In the above formula 1, M １ is Mn, Al or a combination thereof, and M ２ is one or more elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and 0≦x≦0.50, 0.80≦a<1.00, 0<b<0.20, 0<c<0.20, and 0≦d≦0.

20.

5. 5. The positive electrode active material according to claim 4, wherein in Chemical Formula 1, 0.83≦a<1.00, 0<b<0.17, 0<c<0.17, and 0≦d≦0.

17.

6. The positive electrode active material according to claim 1 , wherein the positive electrode active material has a tap density of 2.32 g / cc or greater.

7. A positive electrode slurry comprising the positive electrode active material according to claim 1 .

8. 8. The cathode slurry of claim 7, wherein the cathode slurry has a solids content of 65% to 75% by weight.

9. 8. The positive electrode slurry according to claim 7, wherein the viscosity of the positive electrode slurry measured at 40° C. and a shear rate of 16 rpm is 2,000 cp to 5,000 cp.

10. A positive electrode comprising the positive electrode active material according to claim 1 .

11. A lithium secondary battery comprising the positive electrode according to claim 10.

12. 12. The lithium secondary battery according to claim 11, wherein one cycle is defined as charging at 45° C. at 0.5 C to 4.25 V and discharging at 1.0 C to 3.0 V, and the capacity retention rate of the lithium secondary battery after 50 charge / discharge cycles is 88% or more.

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