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

Abstract

The positive electrode active material according to the present invention is a positive electrode active material comprising a lithium nickel-based oxide that is a single particle consisting of one single nodule, a pseudo-single particle that is a complex of 30 or fewer nodules, or a combination thereof, wherein the positive electrode active material has a D90 of 8.0 μm to 11.5 μm and a Negative Skewness Factor (NSF) expressed by Formula 1 below of 0.20 to 0.35. [Equation 1] NSF = (D50- D10) / Imax In the above Equation 1, D50 is the particle size at the point where the cumulative volume is 50% in the volume cumulative particle size distribution graph of the positive active material, 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 active material, and Imax is the maximum volume fraction in the volume cumulative particle size distribution graph of the positive active material.

Description

Technology Field

[0001] 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 increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly rising. Among these secondary batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used.

[0004] Lithium transition metal composite oxides are used as cathode active materials for lithium secondary batteries, and among them, research and development on lithium nickel-based oxides, which facilitate the realization of high-capacity batteries, is being conducted more actively. However, the secondary particle form had the problem of intensifying crack formation within the cathode active material during charging and discharging.

[0005] To solve the above problems, a technology has been proposed to manufacture a cathode active material in the form of a single particle rather than a secondary particle by increasing the calcination temperature during the manufacture of lithium nickel-based oxides.

[0006] However, single-particle cathode active materials have a problem in that they have low resistance and low output because there are few inter-particle interfaces that serve as pathways for lithium ions and the lithium diffusion path within the particles is long. Therefore, conventionally, the increase in resistance and decrease in output of single-particle cathode active materials were minimized by forming the particles to have an average particle size of 5.0 μm or less.

[0007] However, in order to make the average particle size of the cathode active material in the form of a single particle 5.0㎛ or less, a process of grinding with strong crushing force must be performed, but in this process, a large amount of fine powder is generated, and as a result, there was a problem in that the phase stability of the slurry rapidly deteriorated. The problem to be solved

[0009] The present invention aims to solve the above-mentioned problems by providing a positive electrode active material with excellent phase stability and electrochemical properties of a slurry through the optimization of the particle size distribution of the positive electrode active material, a positive electrode slurry containing the same, a positive electrode, and a lithium secondary battery. means of solving the problem

[0011] In one aspect, 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 pseudo-single particle which is a complex of 30 or fewer nodules, or a combination thereof, wherein the positive electrode active material is D 90 A positive electrode active material is provided having a thickness of 8.0㎛ to 11.5㎛ and a negative skewness factor (NSF) expressed by Formula 1 below of 0.20 to 0.35.

[0012] [Equation 1]

[0013] NSF = (D 50 - D 10 ) / I max

[0014] In the above Equation 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 above-mentioned positive 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 above-mentioned positive active material, and I max is the maximum volume fraction in the volume cumulative particle size distribution graph of the above positive active material.

[0015] The above positive active material is D 50 This can be 5.0㎛ to 7.0㎛.

[0016] The above positive active material is D 10 This can be 2.5㎛ to 3.1㎛.

[0017] The above lithium nickel-based oxide may be represented by the following chemical formula 1.

[0018] [Chemical Formula 1]

[0019] Li 1+x Ni a Co b M 1 c M 2 d O2

[0020] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, and M 2 is one or more 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, 및 0≤d≤0.20일 수 있다.

[0021] In the above Chemical Formula 1, 0.83≤a<1.00, 0 <b<0.17, 0<c<0.17, 및 0≤d≤0.17일 수 있다.

[0022] The above positive active material may have a tap density of 2.32 g / cc or more.

[0024] In another aspect, the present invention provides an anode slurry comprising the anode active material described above.

[0025] The above anode slurry may have a solid content of 65% to 75% by weight.

[0026] The above anode slurry may have a viscosity of 2,000 cp to 5,000 cp measured at a shear rate of 16 rpm at 40°C.

[0028] In another aspect, the present invention provides a positive electrode and a lithium secondary battery comprising the positive electrode active material described above.

[0029] The above lithium secondary battery may have a capacity retention rate of 88% or more after charging and discharging for 50 cycles, with one cycle consisting of charging to 4.25V at 0.5C at 45℃ and discharging to 3.0V at 1.0C. Effects of the invention

[0031] The positive active material according to the present invention is NSF and D 90 By satisfying this specific range, small particles can fill the spaces between relatively large particles, thereby increasing tap density and lowering the viscosity of the slurry to achieve excellent phase stability, and consequently, excellent processability can be achieved.

[0032] In addition, the positive electrode active material according to the present invention comprises single particles and / or pseudo-single particles with excellent particle strength, so that particle breakage is minimal during rolling, thereby enabling excellent lifespan characteristics.

[0033] In addition, when satisfying the particle size distribution according to the present invention, excellent output performance can be achieved with a low resistance increase rate despite having a single particle and / or quasi-single particle form. Specific details for implementing the invention

[0035] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0036] In the present invention, "single particle" is a particle consisting of one single nodule. In the present invention, "pseudo-single particle" refers to a composite particle formed of 30 or fewer nodules.

[0037] In the present invention, "nodule" refers to a particle unit body constituting a single particle and a pseudo-single particle, and the nodule may be a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which grain boundaries are not apparent when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope (SEM). The average grain size of the nodule may be measured as the arithmetic mean of the grain sizes of each nodule measured using a scanning electron microscope (SEM).

[0038] In the present invention, "secondary particle" refers to a particle formed by the aggregation of tens to hundreds of multiple primary particles. More specifically, the secondary particle is an aggregate of 40 or more primary particles.

[0039] The expression “particle” used in the present invention may include any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0040] In the present invention, "D 10 ", "D 50 " and "D 90 " refers to the particle size at 10%, 50%, and 90% of the volume cumulative particle size distribution of the positive electrode active material. The above D 10 , D 50 and D 90 It can be measured using the laser diffraction method. For example, after dispersing the positive active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasound of about 28 kHz at an output of 60 W, and then obtained a volume cumulative particle size distribution graph, and then measured by determining the particle sizes corresponding to 10%, 50%, and 90% of the volume cumulative amount.

[0042] The present invention will be described in more detail below.

[0044] positive electrode active material

[0045] The positive electrode active material according to the present invention comprises a single particle consisting of one single nodule, a pseudo-single particle which is a complex of 30 or fewer nodules, or a combination thereof.

[0046] Lithium nickel-based oxides in the form of single particles and / or similar-single particles have higher particle strength compared to conventional lithium nickel-based oxides in the form of secondary particles in which tens to hundreds of primary particles are aggregated, so there is less particle breakage during rolling.

[0047] In addition, in the case of the lithium nickel-based oxide in the form of a single particle or a quasi-single particle according to the present invention, since the number of sub-components (i.e., nodules) constituting the particle is small, there is less change due to volume expansion and contraction of the primary particles during charging and discharging, and accordingly, the occurrence of cracks inside the particle is significantly reduced.

[0048] In particular, the inventors of the present invention [specifically] the Negative Skewness Factor (NSF) and D 90 It was discovered that when a positive electrode active material satisfying this specific range is applied, the phase stability of the slurry can be improved due to the optimization of particle size distribution, particle breakage during the electrode manufacturing process is minimized, resulting in less gas generation, changes in the crystal structure during the charge / discharge process are minimized, low initial resistance characteristics can be achieved by reducing the diffusion distance of lithium ions within the particles, and energy density can be improved by maximizing tap density.

[0049] The positive active material according to the present invention is D 90 This may be 8.0㎛ to 11.5㎛, 9.0㎛ to 11.0㎛, or 9.5㎛ to 10.5㎛.

[0050] In addition, 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.

[0051] According to the research of the inventors, the above D 90 When both and NSF values ​​satisfy the above range, it was found that the slurry viscosity is generally low and the tap density is high due to the high magnetization of heavy particles and optimization of particle size distribution. On the other hand, the above D 90 If both the and NSF values ​​do not satisfy the above range, it was found that the slurry has high viscosity and low tap density because it has the problems of existing small particles. The above D 90 Or, when only one of the NSF values ​​satisfies the above range, it was found that the viscosity of the slurry is low but the tap density decreases because the particle size distribution optimization is not achieved.

[0052] Specifically, D of the positive active material 90 If this is less than 8.0㎛, the specific gravity of the fine particles increases, which may lower the phase stability of the slurry, and if it exceeds 11.5㎛, there is a large amount of coarse particles, and the distribution of particles with a low degree of single particle size may increase.

[0054] Meanwhile, the positive active material according to the present invention is D 50 This may be 5.0㎛ to 7.0㎛, 5.5㎛ to 6.5㎛, 5.4㎛ to 6.5㎛, or 5.6㎛ to 6.2㎛.

[0055] The single-particle cathode active materials commercialized to date are D 50 It was generally 5.0㎛ or less. However, as such, D 50 In order to form small particles, a grinding process with high crushing intensity must be performed; however, this process generates a large amount of fine powder, which leads to a problem where the phase stability of the slurry rapidly deteriorates. Therefore, in the present invention, compared to the conventional method, D 50By forming it relatively large, the grinding process can be performed at a relatively low crushing pressure, and accordingly, the amount of fine powder generated in the grinding process can be reduced.

[0056] Specifically, D 50 If this is less than 5.0㎛, the amount of fine particles generated increases, which may lower the slurry phase stability, and if it exceeds 7.0㎛, the lithium diffusion pathway within the particles becomes longer, which may lower resistance and output performance.

[0058] Meanwhile, the positive active material according to the present invention is D 10 This may be 2.5㎛ to 3.1㎛, 2.6㎛ to 3.1㎛, or 2.7㎛ to 3.1㎛. D 10 If this is less than 2.5㎛ or exceeds 3.1㎛, the effect of improving the phase stability of the slurry may be negligible.

[0060] Meanwhile, the positive electrode active material according to the present invention may include a lithium nickel-based oxide having a composition as shown in Chemical Formula 1 below.

[0061] [Chemical Formula 1]

[0062] Li 1+x Ni a Co b M 1 c M 2 d O2

[0063] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, and M 2 is one or more 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, 및 0≤d≤0.20일 수 있다.

[0064] The above 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.

[0065] The above a represents the molar ratio of nickel among the total metals excluding 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.

[0066] The above b represents the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <b<0.20, 0<b<0.17, 또는 0<b<0.15일 수 있다.

[0067] The above c is M among the total metals excluding lithium in the lithium nickel-based oxide. 1 Representing the molar ratio of, 0 <c<0.20, 0<c<0.17, 또는 0<c<0.15일 수 있다.

[0068] The above d is M among the total metals excluding lithium in the lithium nickel-based oxide. 2 It represents the molar ratio of the elements, which can be 0≤d≤0.20, 0≤d≤0.17, or 0≤d≤0.15.

[0070] 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 the above range, the amount of fine particles is small, the phase stability of the slurry is improved, and excellent electrochemical properties can be realized.

[0072] The positive active material of the present invention as described above can be manufactured by mixing a positive active material precursor and a lithium raw material and then calcining.

[0074] At this time, the above-mentioned positive electrode active material precursor may be used by purchasing a commercially available positive electrode active material precursor, or it may be manufactured according to a precursor manufacturing method known in the relevant technical field.

[0075] For example, the above precursor can be prepared by introducing an aqueous transition metal solution, an ammonium cation complex formation agent, and a basic compound into a reactor and carrying out a co-precipitation reaction while stirring.

[0076] The above transition metal aqueous solution can be prepared by dissolving a transition metal-containing raw material in a solvent such as water; for example, it can be prepared by dissolving a nickel-containing raw material, a cobalt-containing raw material, or a manganese-containing raw material in water. Additionally, if necessary, the above transition metal aqueous solution may further include an aluminum-containing raw material.

[0077] Meanwhile, the above transition metal-containing raw material may be an acetate, carbonate, nitrate, sulfate, halite, sulfide, or oxide of the transition metal.

[0078] Specifically, the nickel-containing raw material may be, for example, NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or a combination thereof.

[0079] The above cobalt-containing raw material is, for example, CoSO 4, It may be Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O, CoSO4ㆍ7H2O, or a combination thereof.

[0080] The above manganese-containing raw material may be, for example, Mn2O3, MnO2, Mn3O4MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, or a combination thereof.

[0081] The above aluminum-containing raw material may be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halides, or a combination thereof. However, in the case of Al, it is acceptable to add it together with the lithium raw material in the subsequent calcination step without adding it to the transition metal aqueous solution.

[0082] Meanwhile, the ammonium cation complex forming agent may include at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and may be introduced into a reactor in the form of a solution in which said compound is dissolved in a solvent. At this time, the solvent may be water, or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.).

[0083] The above basic compound may be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. In this case, water or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) may be used as the solvent.

[0084] As described above, when an aqueous transition metal solution, an ammonium cation complex forming agent, and a basic compound are introduced into a reactor and stirred, the transition metals in the aqueous transition metal solution co-precipitate, thereby generating precursor particles in the form of transition metal hydroxides.

[0085] At this time, the above-mentioned transition metal aqueous solution, ammonium cation complex forming agent, and basic compound are added in amounts such that the pH of the reaction solution becomes within the desired range.

[0087] When precursor particles are formed in the manner described above, the positive active material precursor is separated from the reaction solution to obtain the positive active material precursor. For example, the reaction solution may be filtered to separate the positive active material precursor from the reaction solution, and then the separated positive active material precursor may be washed and dried to obtain the positive active material precursor. At this time, processes such as grinding and / or classification may be performed as necessary.

[0089] Next, the above-mentioned positive electrode active material precursor and a lithium raw material are mixed and then calcined to produce a lithium nickel-based oxide. At this time, if necessary, an aluminum-containing raw material and / or M 1 Metal-containing raw materials can be mixed together and fired.

[0090] As the above lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides may be used, for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof may be used.

[0091] Meanwhile, the lithium raw material and the cathode active material precursor can be mixed such that the molar ratio of Li to the 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 cathode active material precursor satisfies the above 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 manufactured.

[0093] Meanwhile, the above calcination is performed under conditions that grow the grains of the anode active material so as to satisfy the particle size distribution range of the present invention.

[0094] The appropriate calcination temperature may vary depending on the metal composition in the precursor, for example, when 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.

[0095] Additionally, the above-mentioned firing may be performed under 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 a sufficient amount of oxygen for firing, including an atmospheric atmosphere. In particular, it is preferable to perform the firing in an atmosphere where the oxygen partial pressure is higher than that of an atmospheric atmosphere.

[0097] It is desirable to perform a grinding process after the above-mentioned calcination to control the particle size distribution to a desired level. At this time, the grinding can be performed using general grinding methods known in the art, such as a ball mill or a jet mill. By performing such a grinding process, the particle size of the cathode active material can be controlled more appropriately.

[0098] The grinding above can be performed in 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.

[0099] In addition, the grinding can be performed at a speed range of 1000 rpm to 3000 rpm, 1200 rpm to 2800 rpm, or 1300 rpm to 2500 rpm.

[0100] The positive active material manufactured by performing within the above pressure and speed ranges is D 10 , D 50, and / or D 90 By appropriately controlling to satisfy this certain range, the phase stability and electrochemical properties of the slurry can be excellently realized.

[0102] Anode slurry

[0103] Next, the anode slurry according to the present invention will be described.

[0104] The anode slurry according to the present invention comprises an anode active material according to the present invention. The anode slurry according to the present invention may, together with the anode active material, optionally comprise a conductive material and a binder as needed. Specifically, the anode slurry may be prepared by mixing the anode active material, the conductive material, and / or the binder in a solvent.

[0106] At this time, the above-mentioned positive active material may be included in an amount of 80% to 99% by weight, or 90% to 98% by weight, based on the total solid content of the positive slurry.

[0108] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. 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 fibers; metal powder or metal fibers 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; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.01% to 10% by weight, 0.1% to 9% by weight, or 0.1% to 5% by weight based on the total solid content of the anode slurry.

[0110] The above binder serves to improve the adhesion between positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above 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 anode slurry.

[0112] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the anode slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0114] The anode slurry according to the present invention may have a solid content of 65% to 75% by weight, 67% to 74% by weight, or 69% to 72% by weight.

[0115] The anode 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 a shear rate of 16 rpm at 40°C.

[0117] anode

[0118] Next, the anode according to the present invention will be described.

[0119] The anode according to the present invention comprises an anode active material layer comprising an anode active material according to the present invention. For example, the anode may comprise an anode active material layer formed using the anode slurry according to the present invention described above. Since the anode active material and the anode slurry have been described above, a detailed description is omitted, and only the remaining components will be described in detail below.

[0121] The above positive current collector may include a highly conductive metal, and is not particularly limited as long as it facilitates the adhesion of the positive active material layer and is non-reactive within the voltage range of the battery. The above positive current collector may be, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. It may be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0123] The above-described anode can be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, it can be manufactured by applying the anode slurry onto an anode current collector, followed by drying and rolling.

[0125] Alternatively, the anode may be manufactured by casting the anode slurry onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0127] lithium secondary battery

[0128] Next, a lithium secondary battery according to the present invention will be described.

[0129] Specifically, the above lithium secondary battery comprises a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is identical to the one described above, a detailed description is omitted, and only the remaining components are described in detail below.

[0130] Additionally, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0132] In the above lithium secondary battery, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0133] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0135] The above-mentioned cathode active material layer optionally includes a binder and a conductive material together with the cathode active material.

[0136] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon may be used as the carbon material. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural 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 and coal tar pitch-derived cokes.

[0137] The above-mentioned negative electrode active material may be included 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.

[0139] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, 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, 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.

[0141] The above 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% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, 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, thermal black; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0143] The above-mentioned cathode active material layer may be manufactured by applying a cathode slurry composition, prepared by dissolving or dispersing a cathode active material and optionally a binder and a conductive material in a solvent, onto a cathode current collector and drying it, or by casting the cathode slurry composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0145] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries can be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0147] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0148] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0149] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0151] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the above 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 - It may be at least one selected from the group consisting of, and the lithium salt is, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc. may be used. It is preferable to use the lithium salt within a concentration range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0153] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 10.0 weight% based on the total weight of the electrolyte.

[0155] As described above, a lithium secondary battery comprising a 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 cycles of charging and discharging, with one cycle consisting of charging to 4.25V at 0.5C at 45℃ and discharging to 3.0V at 1.0C.

[0157] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0158] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0159] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0161] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0163] Examples and Comparative Examples

[0164] Example 1

[0165] Positive electrode active material precursor Ni 0.90 Co 0.06 Mn 0.04 (OH)2 and lithium raw material LiOH were mixed in a molar ratio of 1:1, and the mixture was calcined at 810°C for 12 hours.

[0166] Subsequently, the above calcined product is ground for 1 hour under conditions of 2.5 bar and 1400 rpm to obtain the cathode active material LiNi 0.90 Co 0.06 Mn 0.04 O2 was manufactured.

[0167] Example 2

[0168] The above mixture was calcined at 815°C for 12 hours, and the calcined product was ground for 1 hour under conditions of 2.5 bar and 1800 rpm, except that the positive electrode active material was prepared in the same manner as in Example 1.

[0169] Example 3

[0170] The above mixture was calcined at 810°C for 15 hours, and the calcined product was ground for 1 hour under conditions of 2.5 bar and 2400 rpm, except that the positive electrode active material was prepared in the same manner as in Example 1.

[0171] Comparative Example 1

[0172] A positive electrode active material was prepared in the same manner as in Example 1, except that the above mixture was calcined at 830°C for 6 hours and the calcined product was ground for 1 hour under conditions of 3.0 bar and 800 rpm.

[0173] Comparative Example 2

[0174] A positive electrode active material was prepared in the same manner as in Example 1, except that the above mixture was calcined at 840°C for 6 hours and the calcined product was ground for 1 hour under conditions of 3.0 bar and 800 rpm.

[0175] Comparative Example 3

[0176] A positive electrode active material was prepared in the same manner as in Example 1, except that the above mixture was calcined at 750°C for 12 hours and the calcined product was ground for 1 hour under conditions of 2.0 bar and 1600 rpm.

[0177] Comparative Example 4

[0178] A positive electrode active material was prepared in the same manner as in Example 1, except that the above mixture was calcined at 810°C for 12 hours and the calcined product was ground for 1 hour under conditions of 2.5 bar and 800 rpm.

[0180] Experimental Example 1: Particle size distribution of positive electrode active material

[0181] 0.005 g of each positive electrode active material prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was dispersed in a dispersion medium H2O, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) to irradiate with ultrasound of approximately 28 kHz at an output of 60 W to obtain a volume cumulative particle size distribution graph of each positive electrode active material, and using the said graph D 90 , D 50 , D 10 and the NSF value of Equation 1 below was calculated.

[0182] [Equation 1]

[0183] NSF = (D 50 - D 10 ) / I max

[0184] In the above Equation 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 above-mentioned positive 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 above-mentioned positive active material, and I max is the maximum volume fraction in the volume cumulative particle size distribution graph of the above positive active material.

[0185] The results are shown in [Table 1] below.

[0186] D 90 [㎛] D 50 [㎛] D 10 [㎛] NSF Example 1 10.2 5.41 2.80 0.267 Example 2 10.4 6.04 2.30 0.230 Example 3 10.8 6.10 2.57 0.34 Comparative Example 1 6.55 3.96 2.28 0.15 Comparative Example 2 7.06 4.66 3.19 0.13 Comparative Example 3 12.6 8.16 4.86 0.25 Comparative Example 4 8.63 5.64 3.65 0.14

[0188] Experimental Example 2: Tap density of positive electrode active material

[0189] The tap density of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4, respectively, was measured using a tap density tester (Micromeritics GeoPyc 1365).

[0190] Specifically, 10g of the positive active material prepared in Examples 1 to 3 and Comparative Examples 1 to 4, respectively, was filled into a 45cc container, and the tap density was measured by vibrating it horizontally until a force of 108N was applied. The measurement results are shown in [Table 2] below.

[0191] Tap density [g / cc] Example 1 2.53 Example 2 2.57 Example 3 2.48 Comparative Example 1 2.29 Comparative Example 2 1.99 Comparative Example 3 2.37 Comparative Example 4 2.34

[0192] Through [Table 2] above, it can be seen that the cathode active materials of Examples 1 to 3 have a higher tap density than the cathode active materials of Comparative Examples 1 to 4.

[0194] Experimental Example 3: Viscosity of Anode Slurry

[0195] Method for manufacturing anode slurry

[0196] The positive active material, carbon black conductive material, and PVDF binder prepared in Examples 1 to 3 and Comparative Examples 1 to 4, respectively A pre-dispersion with a solid content of 11.2 wt% was prepared by mixing in N-methylpyrrolidone (NMP) in a weight ratio of 97.0 : 1.5 : 1.5. Subsequently, the pre-dispersion and N-methylpyrrolidone (NMP) were mixed in a weight ratio of 97 : 3 to prepare an anode slurry with a solid content of 71 wt%.

[0197] The viscosity of the anode slurry was measured using a viscosity measuring device (BROOKFIFLD DV2TLVTJ0). Specifically, the anode 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].

[0198] Viscosity [cp] Example 1 4160 Example 2 4190 Example 3 3150 Comparative Example 1 5325 Comparative Example 2 16010 Comparative Example 3 2895 Comparative Example 4 3135

[0199] Through the above [Table 3], D falling within the scope of the claim 90 The anode slurry comprising the anode active material prepared in Examples 1 to 3 having and NSF values ​​is D 90It can be seen that the anode slurry containing the anode active material prepared in Comparative Examples 1 and 2, which do not satisfy the claims for both NSF values, has a lower viscosity than the NSF value. Although the NSF value falls within the scope of the claims, D 90 Comparative Examples 3 and D not included in this claim 90 The anode slurry containing the anode active material prepared in Comparative Example 4, which falls within the scope of the claim but whose NSF value does not fall within the scope of the claim, can be confirmed to have a relatively low tap density as observed in Experimental Example 2, as well as a very high resistance increase rate of the lithium secondary battery as described below in Experimental Example 4.

[0201] Experimental Example 4: Electrochemical Characteristics of a Lithium Secondary Battery

[0202] For lithium secondary battery coin half cells prepared as follows using each of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 above, the capacity retention rate (%) and resistance increase rate (%) were measured. The measurement results are shown in [Table 4].

[0204] Specifically, the lithium secondary battery coin half cell was manufactured as follows.

[0205] Each anode slurry prepared in Experimental Example 3 above was applied to one side of an aluminum current collector, dried at 130°C, and then rolled to produce an anode.

[0206] The cathode used lithium metal.

[0207] An electrode assembly was manufactured by interposing a separator between the anode and the cathode, and then the assembly was placed inside a battery case, and an electrolyte was injected into the case to manufacture a battery cell. The electrolyte was prepared by dissolving 1M concentration of LiPF6 in a mixed organic solvent mixed in a volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:1:1, and adding 5 wt% of vinylene carbonate (VC).

[0209] For lithium secondary battery coin half cells containing the positive active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4, the capacity retention rate (%) and resistance increase rate (%) at the 50th cycle were measured by charging and discharging at 3.0V to 4.25V under 0.5C / 1.0C conditions at 45℃ as one cycle.

[0210] Capacity retention rate [%] Resistance increase rate[%] Example 1 89.54 84.32 Example 2 90.22 100.04 Example 3 89.64 84.33 Comparative Example 1 88.85 98.40 Comparative Example 2 89.60 91.60 Comparative Example 3 91.80 97.71 Comparative Example 4 87.71 104.23

[0211] Through [Table 4] above, it can be seen that for the coin half cell containing the positive active material prepared in Examples 1 and 3, the capacity retention rate after high-temperature cycling was at a level equivalent to that of the cell containing the positive active material prepared in Comparative Examples 1 to 4, but the resistance increase rate was lower. For the coin half cell containing the positive active material prepared in Example 2, the resistance increase rate was higher than that of the cell containing the positive active material prepared in Comparative Examples 1 to 4, but as observed in Experimental Examples 2 and 3 above, it can be seen that the tap density of the positive active material is higher and the viscosity of the slurry is lower compared to the comparative examples.

Claims

Claim 1 A positive electrode active material comprising a lithium nickel-based oxide that is a single particle consisting of one single nodule, a pseudo-single particle which is a complex of 30 or fewer nodules, or a combination thereof, wherein the positive electrode active material is D 90 A positive electrode active material having a thickness of 8.0㎛ to 11.5㎛ and a Negative Skewness Factor (NSF) expressed by the following Equation 1 of 0.20 to 0.

35. [Equation 1] NSF = (D 50 - D 10 ) / I max In the above Equation 1, D 50 is the value of the particle diameter measured in μm units at the point where the cumulative volume is 50% in the volume cumulative particle size distribution graph of the above-mentioned cathode active material, and D 10 is the value of the particle diameter measured in μm units at the point where the cumulative distribution is 10% in the volume cumulative particle size distribution graph of the above-mentioned cathode active material, and I max is the value of the maximum volume fraction measured in units of volume % in the volume cumulative particle size distribution graph of the above-mentioned positive active material. Claim 2 In claim 1, the positive active material is D 50 This is a positive electrode active material having a thickness of 5.0㎛ to 7.0㎛. Claim 3 In claim 1, the positive active material is D 10 This positive electrode active material is 2.5㎛ to 3.1㎛ in size. Claim 4 The positive active material of claim 1, wherein 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 In the above chemical formula 1, O2, M 1 is Mn, Al, or a combination thereof, and M 2 is one or more 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, 및 0≤d≤0.20임. Claim 5 In claim 4, in the formula 1, 0.83 ≤ a < 1.00, 0 <b<0.17, 0<c<0.17, 및 0≤d≤0.17인 양극 활물질. Claim 6 In claim 1, the positive active material is a positive active material having a tap density of 2.32 g / cc or more. Claim 7 A positive electrode slurry comprising the positive electrode active material of any one of claims 1 to 6. Claim 8 In claim 7, the anode slurry is an anode slurry having a solid content of 65% to 75% by weight. Claim 9 In claim 7, the anode slurry is an anode slurry having a viscosity of 2,000 cP to 5,000 cP measured at a shear rate of 16 rpm at 40°C. Claim 10 A positive electrode comprising the positive electrode active material of any one of claims 1 to 6. Claim 11 A lithium secondary battery comprising the positive electrode of claim 10. Claim 12 A lithium secondary battery according to claim 11, wherein the lithium secondary battery has a capacity retention rate of 88% or more after charging and discharging for 50 cycles, with one cycle comprising charging to 4.25V at 0.5C at 45℃ and discharging to 3.0V at 1.0C.

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