Positive electrode active material for rechargeable lithium-ion batteries

Abstract

1. A cathode active material for a rechargeable lithium ion battery, the cathode active material comprising Li, Co, O, and optionally M', where M' comprises Al and / or Ti, and optionally one or more elements selected from Ni, Mn, B, Sr, Mg, Nb, W, F, and Zr, a molar ratio of Co to M'+Co (Co / (M'+Co)) is greater than 0.90 as determined by ICP-OES analysis, the cathode active material comprising a first LCO powder and a second LCO powder, both of which are single crystal powders, the first LCO powder having a first median diameter D50A of 12 μm to 25 μm as determined by laser diffraction particle size analysis, the second LCO powder having a second median diameter D50B of 3 μm to 8 μm as determined by laser diffraction particle size analysis, and a volume fraction of the second LCO powder relative to a total volume of the cathode active material is 10% to 40%, as determined by laser diffraction particle size analysis.

Description

[Technical Field]

[0001] This invention relates to a lithium cobalt-based metal oxide (LCO) cathode active material for rechargeable lithium-ion batteries. More specifically, this invention relates to a particulate LCO cathode active material comprising a first LCO powder and a second LCO powder. [Background technology]

[0002] The present invention relates to a single-crystal cathode active material powder for rechargeable lithium-ion batteries (LIBs), comprising a first LCO powder and a second LCO powder. The first LCO powder has a higher median diameter D50 than the second LCO powder, and the first LCO powder is a single crystal.

[0003] Such cathode active materials containing a first LCO powder and a second LCO powder, where the first LCO powder has a higher median diameter D50 than the second LCO powder, are already known, for example, in International Publication 2012 / 171780A1 (hereinafter referred to as WO'780). WO'780 discloses a cathode active powder containing a mixture of large single-crystal LCO powder and small polycrystalline LCO powder. However, when the cathode active material of WO'780 is used in an electrochemical cell, measurements by coin cell floating tests have shown insufficient high-temperature and high-voltage stability. Furthermore, the low powder density results in an even lower electrode density.

[0004] Therefore, the object of the present invention is to achieve low Q float (QF) and Co dissolution (CO) as determined by coin cell float testing. Dis The objective is to provide a positive electrode active material that is stable in use in electrochemical cells at high temperatures and high voltages, as indicated by the small increase in thickness after 4 hours (T4h) determined by a full cell swelling test. The positive electrode active material of the present invention also has a high powder density as measured by compressed density. [Overview of the project] [Means for solving the problem]

[0005] The object of the present invention is achieved by providing the positive electrode active material for a rechargeable lithium-ion battery according to claim 1. As shown by the examples and supported by the results presented in Tables 1 and 2, it is actually observed that better stability and high compressed density can be obtained by using the positive electrode active material of the present invention. Example 1 discloses a positive electrode active material comprising a first LCO powder and a second LCO powder, wherein the first single-crystal LCO powder has a higher median diameter D50 than the second single-crystal LCO powder.

[0006] Further guidance includes drawings to better understand the teaching of the present invention. The drawings are intended to assist the description of the present invention, and are not intended to limit the invention disclosed in the present disclosure. Brief Description of the Drawings

[0007] [Figure 1a] Figs. 1a to 1c respectively show scanning electron microscope (SEM) images of positive electrode active material powders EX1, CEX1, and CEX2. [Figure 1b] Figs. 1a to 1c respectively show scanning electron microscope (SEM) images of positive electrode active material powders EX1, CEX1, and CEX2. [Figure 1c] Figs. 1a to 1c respectively show scanning electron microscope (SEM) images of positive electrode active material powders EX1, CEX1, and CEX2. [Figure 1d] Shows the calculation of the primary particle size of the second LCO from the SEM image of EX1. [Figure 2] Shows SEM and EDS mapping on EX1 particles for elements Co, Al, Ti, and Mg. Ti- and Mg-rich islands are observed on the positive electrode active material particles. [Figure 3] Shows the particle size distribution graph of EX1 deconvoluted into two peaks corresponding to the first and second LCO powders, wherein the x-axis is particle size on a logarithmic scale, and the y-axis is volume fraction. [Figure 4] Shows the graph of swelling tested in a full cell, wherein the x-axis is time in hours, and the y-axis is the increase in cell thickness in percentage. MODE FOR CARRYING OUT THE INVENTION

[0008] Unless otherwise specifically defined, all terms used in the disclosure of the present invention, including technical and scientific terms, have the meanings commonly understood by those skilled in the art to which the present invention pertains.

[0009] Positive electrode active material In a first aspect, the present invention provides a positive electrode active material for a rechargeable lithium ion battery, wherein the positive electrode active material comprises Li (lithium), Co (cobalt), O (oxygen), and optionally M', wherein M' comprises Al and / or Ti, and optionally one or more elements selected from Ni, Mn, B, Sr, Mg, Nb, W, F, and Zr, the molar ratio of Co to M'+Co (Co / (M'+Co)), as determined by ICP-OES analysis, is greater than 0.90 and 1.00 or less, preferably less than 1.00, more preferably 0.99 or less, the positive electrode active material comprises a first LCO powder and a second LCO powder, both of which are single-crystal powders, the first LCO powder has a median diameter D50 of 12 µm to 25 µm as determined by laser diffraction particle size distribution analysis A , the second LCO powder has a median diameter D50 of 3 µm to 8 µm as determined by laser diffraction particle size distribution analysis B , the volume fraction of the second LCO powder relative to the total volume of the positive electrode active material is 10% to 40% as determined by laser diffraction particle size analysis.

[0010] The concept of single-crystal powder is well known in the technical field of positive electrode active materials. It relates mainly to a powder having single-crystal particles. Such a powder is a separate type of powder when compared to polycrystalline powders, which are made mainly of particles that are polycrystalline. A person skilled in the art can easily distinguish between these two classes of powders based on microscopic images.

[0011] Single crystal particles are also known in the art as monolithic particles, integrated particles, or monocrystalline particles.

[0012] Those skilled in the art can easily recognize such powders using a scanning electron microscope (SEM), and therefore a technical definition of single-crystal powder is unnecessary. However, in the context of this invention, single-crystal powder may be defined as powder in which 80% or more of the particles are single-crystal particles. This means at least 45 μm × at least 60 μm (i.e., at least 2700 μm). 2 ), preferably at least 100 μm × 100 μm (i.e., at least 10,000 μm) 2 This can be determined on an SEM image with a field of view of ).

[0013] A single-crystal particle is either an individual crystal or a particle formed from fewer than five, preferably up to three, primary particles that are themselves individual crystals. This can be observed by observing the grain boundaries with a suitable microscopy technique such as a scanning electron microscope (SEM).

[0014] In determining whether a particle is a single-crystal particle, particles with the largest linear dimension observed by SEM that is smaller than 20% of the powder's median diameter D50, as determined by laser diffraction, are ignored. This avoids the inadvertent misconception that some very small particles, such as those on which a polycrystalline coating can be deposited, are not single-crystal particles, even though they are essentially single-crystal.

[0015] Preferably, the positive electrode active material contains M'.

[0016] Preferably, M' contains Al and Ti.

[0017] Preferably, the present invention provides a positive electrode active material according to the first aspect of the invention, wherein the median diameter D50 of the volume ratio of the second LCO powder to the total volume of the positive electrode active material is 10.0 vol% to 35.0 vol%. Preferably, the volume ratio is 15.0 vol% to 30.0 vol%, and more preferably, the volume ratio is equal to 15.0, 20.0, 25.0, 30.0, or any value between any of the foregoing.

[0018] In a preferred embodiment, the positive electrode active material of the first aspect of the present invention, as measured by the BET method, is 0.10 m 2 / g to 0.25 m 2 / g having a specific surface area (SA). Preferably, the positive electrode active material has at least 0.11 m 2 / g, at least 0.12 m 2 / g, at least 0.13 m 2 / g, or further at least 0.14 m 2 / g, or in particular at least 0.15 m 2 / g of SA. Preferably, the positive electrode active material has at most 0.25 m 2 / g, at most 0.24 m 2 / g, at most 0.22 m 2 / g, at most 0.20 m 2 / g of SA.

[0019] In a preferred embodiment, the positive electrode active material of the first aspect of the present invention, determined after applying a uniaxial pressure of 207 MPa for 30 seconds, has a pressed density (PD) of 3.9 g / cm 3 to 4.3 g / cm 3 . Preferably, the positive electrode active material has at least 3.92 g / cm 3 , at least 3.93 g / cm 3 , at least 3.94 g / cm 3 , or further at least 3.95 g / cm 3 , or in particular at least 3.97 g / cm 3 of PD. Preferably, the positive electrode active material has at most 4.30 g / cm 3 , at most 4.20 g / cm 3 , at most 4.15 g / cm 3up to 4.10 g / cm³ 3 It has PD.

[0020] In a preferred embodiment, the positive electrode active material of the first aspect of the present invention has a compressible density to specific surface area (PD / SA) ratio of 19 to 28. Preferably, the positive electrode active material has a PD / SA ratio of at least 20.0, at least 20.5, at least 21.0, or even further at least 21.5, or particularly at least 22.0. Preferably, the positive electrode active material has a PD / SA ratio of up to 27.0, up to 26.0, up to 25.0, or up to 24.5.

[0021] In a preferred embodiment, the positive electrode active material includes particles having Ti and Mg-rich islands on their surface, as determined by SEM-EDS elemental mapping. Preferably, the Ti and Mg-rich islands have a diameter of 0.2 μm to 3.0 μm, as determined by SEM-EDS elemental mapping analysis.

[0022] Preferably, the present invention provides a positive electrode active material according to a first embodiment of the present invention, the positive electrode active material comprising Li, Co, M', and oxygen, where M' comprises Al, Ti, and optionally one or more elements selected from Ni, Mn, B, Sr, Mg, Nb, W, F, and Zr.

[0023] 1st LCO powder In this invention, the first LCO powder has a median diameter D50 of 12 μm to 25 μm, as determined by laser diffraction particle size analysis. A It comprises a single crystal powder having a median diameter D50 A However, the present invention provides a positive electrode active material according to a first aspect of the present invention that is equal to 13, 15, 17, 19, 21, 23, 25 μm, or any value in between.

[0024] Preferably, the present invention relates to a first LCO powder comprising Li, Co, oxygen, and optionally metal M. A ' includes, here, metal M A' comprises Al, Ti, and optionally one or more elements selected from Ni, Mn, B, Sr, Mg, Nb, W, F, and Zr, M A 'Molar ratio of Co to +CO (CO / (M A The present invention provides a positive electrode active material according to a first embodiment of the present invention, wherein the '+CO)) is greater than 0.90 and less than or equal to 1.00, preferably less than 1.00, and more preferably less than or equal to 0.99. The composition can be determined by known analytical methods such as ICP-OES (Inductively coupled plasma-optical emission spectrometry).

[0025] 2nd LCO powder Preferably, the present invention provides a second LCO powder with a median diameter D50 of 3 μm to 8 μm, determined by laser diffraction particle size analysis. B It comprises a single crystal powder having a median diameter D50 B The present invention provides a positive electrode active material according to a first aspect of the present invention, which is equal to 3, 4, 5, 6, 7, 8 μm, or any value in between.

[0026] Preferably, the second LCO powder comprises powder having an average primary particle diameter of 3 μm to 7 μm, as determined by SEM analysis, and more preferably, the average primary particle diameter is equal to 3, 4, 5, 6, 7, or any value in between.

[0027] Preferably, the present invention provides a first LCO powder containing Li, Co, oxygen, and optionally metal M. A ' includes, here, metal M A ' comprises Al, Ti, and optionally one or more elements selected from Ni, Mn, B, Sr, Mg, Nb, W, F, and Zr, and the molar ratio of Co to MA' + CO is (CO / (M A The present invention provides a positive electrode active material according to a first aspect of the present invention, wherein the '+CO)) is greater than 0.90 and less than or equal to 1.00, preferably less than 1.00, and more preferably less than or equal to 0.99. The composition can be determined by known analytical methods such as ICP-OES (inductively coupled plasma emission spectrometry).

[0028] Method for producing cathode active material In a second embodiment, the present invention relates to a method for producing a positive electrode active material, Step 1) Median diameter D50 of 12 μm to 25 μm A A first lithium cobalt-based metal oxide powder having and a median diameter D50 of 3 μm to 8 μm B A step of mixing a second lithium cobalt-based metal oxide powder having and TiO2 to obtain a mixture, wherein both the first lithium cobalt-based metal oxide powder and the second lithium cobalt-based metal oxide powder are single crystal powders, the weight fraction of the second lithium cobalt-based metal oxide to the total weight of the positive electrode active material is 10% to 40%, preferably the weight fraction of the second lithium cobalt-based metal oxide powder to the total weight of the positive electrode active material is 10% to 35%, preferably 15% to 30%, and mixing the two. The present invention provides a manufacturing method comprising step 2) heating the mixture at a temperature of 700°C to 1100°C for 5 to 20 hours. Preferably, the heating temperature is 800°C to 1050°C.

[0029] Batteries containing cathode active material and their use In a third embodiment, the present invention provides a battery cell comprising a positive electrode active material according to a first aspect of the present invention.

[0030] In a fourth aspect, the present invention provides the use of a positive electrode active material according to the first aspect of the present invention in a battery for any one of the following: a portable computer, a tablet, a mobile phone, an electric vehicle, and an energy storage system. [Examples]

[0031] The following embodiments are intended to further clarify the present invention and are not intended to limit its scope.

[0032] 1. Explanation of the analysis method 1.1. Inductively Coupled Plasma Atomic Emission Spectroscopy The composition of the positive electrode active material powder is measured by inductively coupled plasma (ICP) spectroscopy using an Agilent 720 ICP-OES. A 1-gram powder sample is dissolved in 50 mL of high-purity hydrochloric acid (at least 37% by weight of HCl relative to the total weight of the solution) in an Erlenmeyer flask. The flask is covered with a watch glass and heated on a hot plate at 380°C until the powder is completely dissolved. After cooling to room temperature, the solution from the Erlenmeyer flask is poured into a first 250 mL volumetric flask. The first volumetric flask is then filled to the 250 mL mark with deionized water and subsequently homogenized (first dilution). An appropriate amount of solution is pipettered from the first volumetric flask and transferred to a second 250 mL volumetric flask for the second dilution. The second volumetric flask is then filled to the 250 mL mark with internal standard components and 10% hydrochloric acid and homogenized. Finally, this solution is used for ICP-OES measurement.

[0033] 1.2. Compression density Compression density is measured as follows: 3 grams of powder are packed into a pellet die with a diameter "d" of 1.30 cm. A uniaxial load of 207 MPa pressure is applied to the powder in the pellet die for 30 seconds. After the load is released, the thickness "t" of the compressed powder is measured. The pellet density (PD) is:

[0034]

number

[0035] 1.3. Scanning Electron Microscopy - Dispersive X-ray Spectroscopy (SEM-EDS) The morphology of the positive electrode active material is analyzed using scanning electron microscopy (SEM) technology. This measurement is performed at 25°C at a density of 9.6 × 10⁻⁶. -5 The procedure is performed in a high vacuum environment of Pa using a JEOL JSM7100F.

[0036] The concentrations of Co, Al, Mg, and Ti on the surface of secondary particles of the cathode material are analyzed by energy-dispersive X-ray spectroscopy (EDS). The EDS is a 50mm Oxford Instruments machine. 2The analysis is performed using a JEOL JSM 7100F SEM instrument equipped with an X-MaxN EDS sensor. Quantitative elemental analysis of the positive electrode active material particles can be obtained from the EDS analysis.

[0037] 1.4.Particle size distribution 1.4.1. Measurement of particle size by laser diffraction The particle size distribution (PSD) of the positive electrode active material powder is measured by laser diffraction particle size analysis using a Malvern Mastersizer 3000 equipped with a Hydro MV wet dispersion attachment after each powder sample is dispersed in an aqueous medium. To improve powder dispersion, sufficient ultrasonic irradiation and stirring are applied, and an appropriate surfactant is introduced. The median diameter D50 is defined as the particle size at 50% of the cumulative volume % distribution obtained from measurements using the Malvern Mastersizer 3000 with Hydro MV.

[0038] The first and second LCO particle sizes can be visually determined from the peaks in the measured particle size distribution, for example, by laser diffraction. The volume fraction of the second LCO powder can be determined by the ratio of the area under the curve of the second LCO powder to the total area under the curve of both the first and second LCO powders. If necessary, known peak deconvolution algorithms may be used.

[0039] 1.4.2. Particle size analysis by SEM The diameter of the primary particles is calculated using ImageJ software (ImageJ 1.52a, National Institutes of Health, USA) according to the following procedure. Step 1) Open the file containing the SEM image of the cathode active material at 1000x magnification. Step 2) Set the scale according to the magnification of the SEM. Step 3) For at least 50 particles, use the polygonal selection tool to draw lines along the edges of the primary particles. Particles at the edges of the image should be excluded if they have been truncated. Step 4) Measure the area of ​​the selected, drawn primary particles using the measurement settings and area box. Step 5) Assuming the particles are spherical,

[0040]

number

[0041] Figure 1d shows an example of calculating the primary particle size of the second LCO of EX1 using this method.

[0042] 1.5.Surface area The specific surface area (SA) of the positive electrode active material is measured using the Brunauer-Emmett-Teller (BET) method with a Micromeritics Tristar II 3020. To remove adsorbed chemical species, the powder sample is heated under nitrogen (N2) gas at 300°C for 1 hour before measurement. The dried powder is placed in a sample tube. The sample is then degassed at 30°C for 10 minutes. In this apparatus, nitrogen adsorption tests are performed at 77K. By obtaining the nitrogen isothermal adsorption / desorption curve, m 2 The total specific surface area of ​​the sample is derived in units of / g.

[0043] 1.6. Coin Cell 1.6.1. Preparation of coin cells The coin cells used in floating test analysis are assembled according to the following process.

[0044] Step 1) Cathode preparation: A solid containing LCO cathode active material powder, conductor (Super P, Timcal), and binder (KF#9305, Kureha) in a weight ratio of 90:5:5 is mixed with a solvent (NMP, Sigma-Aldrich) using a high-speed homogenizer to obtain a homogenized slurry. The homogenized slurry is spread onto one side of aluminum foil using a doctor blade coater with a 230 μm gap. The slurry-coated aluminum foil is dried in a 120°C oven, then pressed using a calendering tool, and dried again in a vacuum oven to completely remove the solvent.

[0045] Step 2) Assembly of the coin cell: The coin cell is assembled in a glove box filled with inert gas (argon). For discharge capacity analysis, one separator (Celgard) is placed between the cathode and the graphite used as the anode. For floating tests, two separators are placed between the cathode and the anode. 1M LiPF6 in EC:DMC (1:2 by volume) is used as the electrolyte and is dropped between the separator and the electrode. The coin cell is then completely sealed to prevent electrolyte leakage.

[0046] 1.6.2. Floating Test Analysis Floating tests analyze the crystal stability of LCO compounds under high temperature and high voltage conditions.

[0047] The fabricated coin cell will be tested according to the following charging protocol: First, it will be charged to 4.5V in a constant current mode using a C / 20 rate (1C = 160mAh / g) in a 50°C chamber. Then, the coin cell will be left at a constant voltage (4.5V) for 5 days (120 hours).

[0048] Once a side reaction or metal elution occurs, the voltage drops. Electrochemical instruments automatically compensate for the (lost) current to maintain a constant voltage. Therefore, the recorded current is an indicator of the side reactions progressing during the cycle.

[0049] The specific floating capacity (QF) is the total capacity (mAh / g) during the floating test. After the floating test, the coin cell is disassembled. The anode and the separator (adjacent to the anode) are analyzed by ICP-OES for metal leaching. The measured cobalt content is normalized by the total amount of active material in the electrode to obtain the specific cobalt leaching value.

[0050] 1.7. Full Cell 1.7.1. Explanation of Full Cell Preparation A 2000mAh pouch-type battery is prepared as follows: Positive electrode material powder, carbon black (LITX200, Carbot) and MWCNT (LB-107, Cano) as positive electrode conductive agents, and polyvinylidene fluoride (PVdF, S5130, commercially available from Solvay) as a positive electrode binder are added to NMP (N-methyl-2-pyrrolidone) as a dispersion medium. The mass ratio of positive electrode material powder, carbon black, MWCNT, and binder is 97.8 / 0.5 / 0.7 / 1. The mixture is then kneaded to prepare a positive electrode mixture slurry. Next, the obtained positive electrode mixture slurry is applied to both sides of a positive electrode current collector made of 20μm thick aluminum foil for a 2000mAh pouch-type battery. The load weight of the positive electrode active material is approximately ~17mg / cm². 2 Next, the electrodes are dried and calendered using a pressure of 5 MPa and a press roll gap of 10 μm. A typical electrode density is 4.1 g / cm³. 3 Furthermore, an aluminum plate, which functions as a positive electrode current collector tab, is arc-welded to the end of the positive electrode.

[0051] A commercially available negative electrode is used. Briefly, a mixture of graphite, carbon black (Super P), CMC (carboxymethylcellulose-sodium), and SBR (styrene-butadiene rubber) in a mass ratio of 96 / 1 / 1.5 / 2.5 is applied to both sides of the copper foil. A nickel plate, which functions as a negative electrode current collector tab, is arc-welded to the end of the negative electrode.

[0052] A wound electrode body is obtained by winding a sheet-shaped positive electrode, a sheet-shaped negative electrode, and a sheet-shaped conventional separator (for example, a ceramic-coated separator with a thickness of 13 μm and a porosity of 30% to 50%, preferably 39 to 44%) sandwiched between them using a winding rod. Next, the wound electrode body and electrolyte are placed in an aluminum laminate pouch in a dry air chamber with a dew point of -50°C to produce a flat pouch-type rechargeable lithium battery. The design capacity of the rechargeable battery is 2000 mAh when charged to 4.45 V.

[0053] Immerse the battery in a non-aqueous electrolyte at room temperature for 8 hours. Pre-charge the battery to 15% of its theoretical capacity and age it at room temperature for 1 day. Then, degas the battery and seal the aluminum pouch. Prepare the battery for use as follows: Charge the battery in CC mode (constant current) with a current of 0.2C (where 1C = 2000mA) up to 4.45V, then in CV mode (constant voltage) until it reaches a cutoff current of C / 20. Then, discharge the battery in CC mode at a rate of 0.2C to a cutoff voltage of 3.0V.

[0054] 1.7.2. Swelling Test Method The pouch-type batteries prepared using the above method were fully charged to 4.45V, heated in an oven to 90°C, and then left for 20 hours. At 90°C, the charged cathode reacts with the electrolyte to generate gas. This gas causes expansion. The change in thickness ((thickness before and after storage) / thickness before storage) was recorded every hour.

[0055] 2. Examples and Comparative Examples Example 1 The positive electrode active material labeled EX1 is prepared according to the following steps. Step 1) Prepare EX1-A, a single-crystal cathode active material, according to the procedure below. a. First mixture: Co3O4 powder having a D50 of 20 μm is mixed with Li2CO3, Al2O3, and MgO to obtain a first mixture with a lithium-to-metal (Li / (Al+Co)) ratio of 1.05, an Al / Co molar ratio of 0.015, and a Mg / Co molar ratio of 0.005. b. First heating: The first mixture from step 1.a) is heated in a furnace under a dry air atmosphere at 1050°C for 12 hours to obtain the first heated powder. c. Post-processing: The first heated powder from step 1.c) is pulverized and sieved to obtain EX1-A.

[0056] Step 2) Prepare EX1-B, a single-crystal cathode active material, according to the procedure below. a. Second mixture: Co3O4 powder having a D50 of 6 μm is mixed with Li2CO3, Al2O3, and MgO to obtain a second mixture with a lithium-to-metal (Li / (Al+Co)) ratio of 1.05, an Al / Co molar ratio of 0.015, and a Mg / Co molar ratio of 0.005. b. Second heating: The second mixture from step 2.a) is heated in a furnace under a dry air atmosphere at 1050°C for 12 hours to obtain the second heated powder. c. Post-processing: The second heated powder from step 1.c) is pulverized and sieved to obtain EX1-B.

[0057] Step 3) Prepare EX1, which is a mixture of single crystal EX1-A and single crystal EX1-B, according to the procedure below. Third mixture: EX1-A, EX1-B, COH, and TiO2 are mixed to obtain a third mixture with a weight ratio of EX1-A:EX1-B = 80%:20%, a Li / (Co+Al) molar ratio of 1.00, and a Ti / Co molar ratio of 0.0015. COH is a Co with a median diameter D50 of 100 nm. 0.980 Al 0.015 Mg 0.005 It is (OH)2 powder. b. Third heating: The third mixture from step 4.a) is heated in a furnace under a dry air atmosphere at 1050°C for 12 hours to obtain the third heated powder. c. Post-processing: The third heated powder from step 4.c) is pulverized and sieved to obtain EX1-B.

[0058] Comparative Example 1 The positive electrode active material labeled CEX1 is prepared according to the following steps. Step 1) Prepare the single-crystal cathode active material CEX1-A according to the procedure below. a. First mixture: Co3O4 powder having a D50 of 2 μm is mixed with Li2CO3, MgO, and TiO2 to obtain a first mixture with a lithium-to-metal (Li / Co) ratio of 1.06, a Mg / Co molar ratio of 0.0025, and a Ti / Co molar ratio of 0.0008. b. First heating: The first mixture from step 1.a) is heated in a furnace under a dry air atmosphere at 1000°C for 12 hours to obtain the first heated powder. c. Post-processing: The first heated powder from step 1.c) is pulverized and sieved to obtain CEX1-A.

[0059] Step 2) Prepare CEX1, which is a mixture of CEX1-A and Co3O4, according to the procedure below. a. Second mixture: CEX1-A, Li2CO3, Co3O4, MgO, TiO2, and Al2O3 are mixed to obtain a second mixture with a Li / Co molar ratio of 1.00, a Mg / Co molar ratio of 0.01, a Ti / Co molar ratio of 0.0028, and an Al / Co molar ratio of 0.01, where 13 mol% of Co is added compared to the cobalt in CEX1-A. b. Second heating: The second mixture from step 2.a) is heated in a furnace under a dry air atmosphere at 980°C for 10 hours to obtain the second heated powder. c. Post-processing: The second heated powder from step 2.c) is pulverized and sieved to obtain CEX1.

[0060] CEX1 belongs to WO'780.

[0061] Comparative Example 2 The positive electrode active material labeled CEX2 is prepared according to the following steps. Step 1) Prepare the single-crystal cathode active material CEX2-A according to the procedure below. a. First mixture: Co3O4 powder having a D50 of 20 μm is mixed with Li2CO3, Al2O3, and MgO to obtain a first mixture with a lithium-to-metal (Li / (Al+Co)) ratio of 1.03, an Al / Co molar ratio of 0.015, and a Mg / Co molar ratio of 0.005. b. First heating: The first mixture from step 1.a) is heated in a furnace under a dry air atmosphere at 1050°C for 12 hours to obtain the first heated powder. c. Post-processing: The first heated powder from step 1.c) is pulverized and sieved to obtain CEX2-A.

[0062] Step 2) Prepare CEX2-B, which is Co3O4 containing Al and Mg, according to the procedure below. a. Second mixture: Co3O4 powder having a D50 of approximately 2 μm is mixed with Al2O3 and MgO to obtain a second mixture with an Al / Co molar ratio of 0.015 and a Mg / Co molar ratio of 0.005. b. Second heating: The mixture from step 2.a) is heated in a furnace under a dry air atmosphere at 800°C for 12 hours to obtain CEX2-B.

[0063] Step 3) Prepare CEX2, which is a mixture of single crystal CEX2-A and polycrystalline CEX2-B, according to the procedure below. a. Third mixture: CEX2-A, CEX2-B, Li2CO3, and TiO2 are mixed to obtain a third mixture with a Li / (Co+Al) molar ratio of 1.00 and a Ti / Co molar ratio of 0.0015, where 15 mol% of Co is added compared to the cobalt in CEX2-A. b. Third heating: The third mixture from step 3.a) is heated in a furnace under a dry air atmosphere at 980°C for 12 hours to obtain the second heated powder. c. Post-processing: The second heated powder from step 3.c) is pulverized and sieved to obtain CEX2.

[0064] [Table 1]

[0065] [Table 2]

[0066] Table 1 summarizes the first and second LCO powder components of EX1, CEX1, and CEX2. EX1 contains the first and second LCO powders having the single-crystal morphology shown in the SEM image in Figure 1a. On the other hand, CEX1 and CEX2 are mixtures of the first single-crystal LCO powder and the second polycrystalline LCO powder. SEM images of CEX1 and CEX2 are shown in Figures 1b and 1c, respectively.

[0067] Figure 4 shows the particle size distribution graph of EX1. From the graph, the first median diameter D50 A It is approximately 21 μm, and the second median diameter D50 B The particle size is approximately 6 μm. The volume fraction of the second LCO powder is 19.2% by volume.

[0068] Table 2 summarizes the composition, specific surface area, compressive density, and electrochemical test results of the examples and comparative examples. EX1 exhibits the lowest specific surface area SA compared to CEX1 and CEX2. A low specific surface area indicates a low QF and low Co Dis This is related to high stability at high temperatures and voltages, as indicated by its low T4h. In addition, EX1 exhibits a higher compressible density PA compared to CEX1 and CEX2. The superior performance of EX1 in terms of stability and density is due to its compositional mixture containing large first LCO single crystal powder and small second LCO single crystal powder.

[0069] It is concluded that EX1 satisfies the objective of the present invention to provide a cathode active material that is stable in high-temperature and high-voltage electrochemical cell applications and has a high compressibility density.

Claims

1. A positive electrode active material for rechargeable lithium-ion batteries, The positive electrode active material consists of Li, Co, O, and M', where M' includes Al, Mg, and Ti, and optionally one or more elements selected from Ni, Mn, B, Sr, Nb, W, F, and Zr, and the molar ratio of Co to M' + Co (Co / (M' + Co)) is greater than 0.90 as determined by ICP-OES analysis. As determined by ICP-OES analysis, the molar ratio of Al to Co (Al / Co) is 0.001 to 0.030, the molar ratio of Mg to Co (Mg / Co) is 0.001 to 0.020, and the molar ratio of Ti to Co (Ti / Co) is 0.001 to 0.

005. The positive electrode active material includes a first LCO powder and a second LCO powder, both of which are single crystal powders. The first LCO powder has a first median diameter D50 of 12 μm to 25 μm, determined by laser diffraction particle size analysis. Ａ It has, The second LCO powder has a second median diameter D50 of 3 μm to 8 μm, determined by laser diffraction particle size analysis. Ｂ It has, A positive electrode active material in which the volume fraction of the second LCO powder relative to the total volume of the positive electrode active material is 10% to 40%, as determined by laser diffraction particle size analysis.

2. The positive electrode active material according to claim 1, wherein the positive electrode active material comprises M'.

3. The positive electrode active material according to claim 1, wherein M' comprises Al and Ti.

4. The positive electrode active material according to claim 1, wherein the second LCO powder comprises powder having an average primary particle diameter of 3 μm to 7 μm as determined by SEM analysis.

5. The positive electrode active material was determined by BET analysis, and is 0.10 m ２ / g ~ 0.25m ２ The positive electrode active material according to claim 1, having a specific surface area of ​​1 / g.

6. The positive electrode active material was subjected to a uniaxial pressure of 207 MPa for 30 seconds, resulting in a concentration of 3.9 g / cm³. ３ ~4.3 g / cm ３ The positive electrode active material according to claim 1, having a compressible density of .

7. The positive electrode active material according to claim 6, wherein the ratio of compressible density to specific surface area is 19.0 to 28.

0.

8. The positive electrode active material according to claim 1, wherein the positive electrode active material contains M', and M' contains Ti and / or Mg.

9. The positive electrode active material according to claim 1, wherein the first LCO powder includes particles having Ti and / or Mg-rich islands on the surface of the particles as determined by SEM-EDS elemental mapping.

10. The positive electrode active material according to claim 1, wherein the first LCO powder comprises particles having Ti and Mg-rich islands on the surface of the particles as determined by SEM-EDS elemental mapping.

11. The positive electrode active material according to claim 10, wherein the Ti and Mg-rich islands have a diameter of 0.2 μm to 3.0 μm as determined by SEM analysis.

12. The second median diameter D50 Ｂ The positive electrode active material according to claim 1, wherein the particle size is 5 μm to 7 μm.

13. The positive electrode active material according to claim 1, wherein the volume fraction of the second LCO powder relative to the total volume of the positive electrode active material is 15% to 30%.

14. The positive electrode active material according to claim 1, wherein the positive electrode active material has a specific stagnant capacity of 10 mAh / g to 150 mAh / g, as determined by electrochemical analysis over 120 hours at 4.5 V and 50°C.

15. A method for producing a positive electrode active material according to any one of claims 1 to 14, comprising the following steps: 1) a first lithium cobalt-based metal oxide powder having a median diameter D50 of 12 μm to 25 μm Ａ and a second lithium cobalt-based metal oxide powder having a median diameter D50 of 3 μm to 8 μm Ｂ and TiO ２ to obtain a mixture, wherein both the first lithium cobalt-based metal oxide powder and the second lithium cobalt-based metal oxide powder are single crystal powders, and a weight fraction of the second lithium cobalt-based metal oxide relative to a total weight of the positive electrode active material is 10% to 40%. 2) A method comprising the step of heating the mixture at a temperature of 700°C to 1100°C for 5 to 20 hours.

16. Step 1) median diameter D50 of 12 μm to 25 μm Ａ A first lithium cobalt-based metal oxide powder having a median diameter D50 of 3 μm to 8 μm Ｂ A second lithium cobalt-based metal oxide powder having and a median diameter D50 of less than 300 nm Ｃ A Co-based compound having TiO ２ The method according to claim 15, comprising the step of mixing a first lithium cobalt-based metal oxide powder and a second lithium cobalt-based metal oxide powder to obtain a mixture, wherein both the first lithium cobalt-based metal oxide powder and the second lithium cobalt-based metal oxide powder are single crystal powders, and the weight fraction of the second lithium cobalt-based metal oxide with respect to the total weight of the positive electrode active material is 10% to 40%.

17. The aforementioned Co-based compound has a median diameter D50 of less than 150 nm. Ｃ The method according to claim 16, wherein the Co-based compound comprises Al and / or Mg.

18. A battery cell comprising the positive electrode active material described in any one of claims 1 to 14.

19. Use of the battery according to claim 18 in any of the following: a portable computer, a tablet, a mobile phone, a power tool, an electric vehicle, and an energy storage system.

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