Positive electrode active material for rechargeable lithium-ion batteries

Abstract

The present invention relates to a positive electrode active material in a rechargeable lithium ion battery having a differential concentration of cobalt and nickel between the center and the edge of the secondary particles and a specific range of crystallite sizes.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material suitable for use in rechargeable lithium-ion secondary batteries, comprising secondary particles having a difference in cobalt and nickel concentrations between the center and edge of the secondary particles, and containing crystallite sizes within a specific range. [Background technology]

[0002] To meet the requirements for batteries used in automobiles and portable electronic devices, there is a need for Ni-rich NMC cathode materials with improved electrochemical properties. Within the framework of this invention, a Ni-rich NMC compound or material is a LiM'O2 cathode material having a molar content of at least 75 mol% of Ni.

[0003] First cycle efficiency (E F ) is one of the important indicators for evaluating the performance of secondary batteries. F This value is obtained by dividing the initial discharge capacity (DQ1) by the initial charge capacity (CQ1) and multiplying by 100 (%). High E F Secondary batteries with the following characteristics are likely to have low lithium-ion loss during the initial charge and discharge cycle and a large capacity per unit volume and weight. Therefore, secondary batteries should have the highest possible E F It is desirable to stop.

[0004] Many efforts already exist to improve the electrochemical properties of cathode active materials, such as the core-shell structure of cathode active materials. In this regard, Umicore's International Publication No. 2020083980 discloses a cathode active material having improved electrochemical properties, with a high Co content and low Ni content in the cathode active material shell. However, the Ni content of the cathode active material in Example 1 (EX1-P1) of International Publication No. 2020 / 083980 is only 74 mol% compared to the total metal content, and the Ni content of the cathode material in Example 2 (EX2-P1) of International Publication No. 2020 / 083980 is 73 mol% compared to the total metal content. Comparative Example 2 of International Publication No. 2020 / 083980 discloses a cathode active material (CEX2-P1) having a Ni content of 76 mol% compared to the total metal content of the cathode active material. However, CEX2-P1 is prepared from a metal hydroxide precursor having a shell Co content of less than 50 mol% compared to the total metal content in the shell. Therefore, the positive electrode active material CEX2-P1 is thought to lack a core-shell structure due to Co diffusion during the heating step. This explains why CEX2-P1 has inferior electrochemical properties.

[0005] While achieving good electrochemical properties, manufacturing costs can still be improved. A key cost factor is the total concentration of Co in the cathode active material. [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the present invention provides excellent electrochemical properties, such as an initial discharge capacity (DQ1) higher than 205 mAh / g and a first cycle efficiency (E) higher than 90%. F The objective is to provide a Ni-rich cathode active material (i.e., containing at least 75 mol% Ni) having the following characteristics. [Means for solving the problem]

[0007] This object is a cathode active material suitable for a lithium-ion rechargeable battery, containing Li, M', and oxygen, where M' is Ni with a content x of 75.0 mol% to 95.0 mol% with respect to M', Co with a content y of 1.0 mol% to 25.0 mol% with respect to M', Mn with a content z of 0.0 mol% to 25.0 mol% with respect to M', Al with a content b of 0.0 mol% to 5.0 mol% with respect to M', an element other than Li, Ni, Mn, Co, O, and Al with a content a of 0.0 mol% to 5.0 mol% with respect to M' including the contents x, y, z, a, and b are measured by ICP, x + y + z + a + b is 100.0 mol%, the cathode active material includes secondary particles composed of a plurality of primary particles, the cathode active material has a Ni content Ni and a Co content Co measured by cross-sectional EDS (CS-EDS) at the edge of the secondary particles of the cathode active material, edge and edge the Ni and Co contents are expressed as mol% with respect to the sum of the Ni, Mn, and Co contents measured by CS-EDS at the edge of the secondary particles of the cathode active material, the cathode active material has a Ni content Ni and a Co content Co measured by CS-EDS at the center of the secondary particles of the cathode active material, center and center the Ni and Co contents are expressed as mol% with respect to the sum of the Ni, Mn, and Co contents measured by CS-EDS at the center of the secondary particles of the cathode active material, ratio Ni edge / Ni center < 0.98, ratio Co edge / Co center > 1.10, the secondary particles have an average crystallite size of at least 15 nm and a maximum of 40 nm determined by XRD, is achieved by providing a cathode active material.

[0008] In this context, the positive electrode active material is defined as a material that is electrochemically active at the positive electrode. The active material should be understood as a material that, when exposed to voltage changes over a predetermined period, can capture and release Li ions.

[0009] The present invention relates to the following embodiments.

[0010] Embodiment 1 In a first aspect, the present invention relates to a positive electrode active material suitable for lithium-ion rechargeable batteries, comprising Li, M' and oxygen, wherein M' is Ni with an content of x of 75.0 mol% to 95.0 mol% relative to M', Co, with a content of y of 1.0 mol% to 25.0 mol% relative to M'. Mn with a content of 0.0 mol% to 25.0 mol% relative to M', Al content of 0.0 mol% to 5.0 mol% relative to M', Elements other than Li, Ni, Mn, Co, O, and Al, present in a content of 0.0 mol% to 5.0 mol% a relative to M'. Includes, The contents x, y, z, a, and b were measured by ICP. x+y+z+a+b is 100.0 mol%, The positive electrode active material contains secondary particles consisting of multiple primary particles. The Ni content of the positive electrode active material is measured by cross-sectional EDS (CS-EDS) at the edge of the secondary particles of the positive electrode active material. edge and Co content edge The Ni and Co content is expressed as mol% of the sum of the Ni, Mn, and Co content, as measured by CS-EDS at the edge of the secondary particles of the positive electrode active material. The Ni content of the positive electrode active material is measured by CS-EDS at the center of the secondary particles of the positive electrode active material. center and Co content centerThe Ni and Co content is expressed as mol% of the sum of the Ni, Mn, and Co content, as measured by CS-EDS at the center of the secondary particles of the positive electrode active material. Ratio Ni edge / Ni center <0.98, ratioCo edge / Co center >1.10, The secondary particles, as determined by XRD, have an average crystallite size of at least 15 nm and a maximum of 40 nm. We provide a positive electrode active material.

[0011] Preferably, the Ni content is x ≥ 77.0 mol%, and more preferably x ≥ 80.0 mol%, relative to M'.

[0012] Preferably, the Ni content is x ≤ 93.0 mol%, and more preferably x ≤ 91.0 mol%, relative to M'.

[0013] Preferably, the Co content y > 2 mol%, more preferably y ≥ 3.0 mol%, and even more preferably y ≥ 5.0 mol% relative to M'.

[0014] Preferably, the Mn content z > 1 mol%, more preferably ≥ 3.0 mol%, and even more preferably z ≥ 4.0 mol% relative to M'.

[0015] In another embodiment, the amount of Ni with content x is 80 mol% to 93 mol% relative to M', and the amount of Co with content y is 1.0 mol% to 20.0 mol% relative to M'.

[0016] In a preferred embodiment, the positive electrode active material of the present invention comprises lithium transition metal oxide powder.

[0017] Embodiment 2 In the second embodiment, preferably according to Embodiment 1, the positive electrode active material of the present invention contains Al in an amount b of 0.1 mol% to 3.0 mol% relative to M'.

[0018] Preferably, the Al content b relative to M' is ≥0.15 mol%, more preferably b ≥0.2 mol%, and most preferably b ≥0.3 mol%.

[0019] Preferably, with respect to M', the Al content b is ≤2.0 mol%, more preferably b ≤1.0 mol%, and most preferably b ≤0.5 mol%.

[0020] Embodiment 3 In the third embodiment, preferably according to Embodiment 1 or Embodiment 2, the positive electrode active material of the present invention has a Ni content measured by cross-sectional EDS (CS-EDS) at the edge of the secondary particles of the positive electrode active material. edge and Co content edge The Ni and Co content is expressed as a mole fraction compared to the sum of the Ni, Mn, and Co content, which is measured by CS-EDS at the edge of the secondary particles of the positive electrode active material. The Ni content of the positive electrode active material is measured by CS-EDS at the center of the secondary particles of the positive electrode active material. center and Co content center The Ni and Co content is expressed as a mole fraction compared to the sum of the Ni, Mn, and Co content measured by CS-EDS at the center of the secondary particles of the positive electrode active material. Ratio Ni edge / Ni center <0.97 ratioCo edge / Co center It is >1.15.

[0021] In the framework of this invention, the outer edge of the secondary particles of the positive electrode active material is the boundary or outer limit that distinguishes the secondary particles from their external environment. The mole fraction of elements at the center of the secondary particles is determined by EDS measurement of a cross-sectional sample at the center of the secondary particles. The center of the secondary particles is the center point of the longest axis of the secondary particles in the cross-section.

[0022] Secondary particles collected for CS-EDS measurement typically have a diameter of D50 ± 0.5 μm, as determined by particle size distribution analysis.

[0023] Preferably, Limited edge / Ni center The value is ≤0.96.

[0024] Preferably, Limited edge / Ni center >0.8, and more preferably Ni edge / Ni center It is >0.85.

[0025] Preferably, Co edge / Co center >1.20, and more preferably Co edge / Co center It is >1.30.

[0026] Preferably, Co edge / Co center <1.8, and more preferably Co edge / Co center <1.7.

[0027] Preferably, Limited edge and Ni center The difference between and is at least 5 mol%, Co edge and Co center The difference between them is at least 2 mol%, which causes Ni and Co to exhibit a concentration gradient from the periphery to the center of the secondary particles of the positive electrode active material.

[0028] Preferably, specific Co edge / C 3 / 4 is, relative Co edge / Co center Smaller, here, C 3 / 4 This refers to the Co content, expressed as mol% relative to the sum of Ni, Mn, and Co content, measured by CS-EDS at 3 / 4 of the distance from the edge of the secondary particle to the center of the secondary particle.

[0029] Preferably, relative to theedge / Ni 3 / 4 is, Specific Ni edge / Ni center Larger, here, Ni 3 / 4 This refers to the Ni content, expressed as mol% relative to the sum of Ni, Mn, and Co content, measured by CS-EDS at 3 / 4 of the distance from the edge of the secondary particle to the center of the secondary particle.

[0030] Preferably, the positive electrode active material has a cobalt gradient (mol% / μm), The cobalt gradient is 0.2 ≤ cobalt gradient ≤ 1.0, preferably 0.4 ≤ cobalt gradient ≤ 0.9, and the cobalt gradient is expressed by the following equation:

[0031]

number

[0032] Within the framework of this invention, the material has a concentration gradient, where there is a difference in Co and Ni concentrations between the center and the periphery, and the Ni and Co content is expressed as mol% of the sum of Ni, Mn, and Co content, measured by CS-EDS at the center or periphery of the secondary particles of the positive electrode active material.

[0033] Preferably, the Mn content is measured by cross-sectional EDS (CS-EDS) at the edge of the secondary particles of the positive electrode active material. edge The Mn content is expressed as mol% relative to the sum of the Ni, Mn, and Co content, measured by CS-EDS at the edge of the secondary particles of the positive electrode active material, and Mn edge It is greater than 0 mol%.

[0034] Embodiment 4 In a fourth aspect, preferably according to embodiments 1-2, the cathode active material of the present invention typically comprises secondary particles having an average crystallite size of at least 15 nm, as determined by XRD.

[0035] Preferably, the secondary particles of the positive electrode active material have an average crystallite size of at least 17 nm, and more preferably at least 20 nm, as determined by XRD.

[0036] Preferably, the secondary particles of the positive electrode active material have an average crystallite diameter of up to 40 nm, more preferably up to 38 nm, and most preferably up to 35 nm, as determined by XRD.

[0037] Embodiment 5 In the fifth aspect, preferably according to embodiments 1 to 4, the positive electrode active material of the present invention contains elements other than Li, O, Ni, Co, Mn, and Al, and the content of a relative to M' is 0.01 mol% to 5.0 mol%, preferably a is 0.1 mol% to 4 mol%.

[0038] In another embodiment, the element other than Li, O, Ni, Co, Mn, and Al is preferably selected from the group consisting of B, Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, W, Zn, and Zr, and most preferably S.

[0039] In a further embodiment, the positive electrode active material of the present invention contains S in a content a of preferably 0.6 mol% to 3.0 mol%, most preferably 0.65 mol% to 2.0 mol%, and even more preferably 0.7 mol% to 1.5 mol%, relative to M'.

[0040] Embodiment 6 In a sixth aspect, the present invention provides a battery comprising the positive electrode active material of the present invention.

[0041] Embodiment 7 In a seventh aspect, the present invention provides the use of a battery according to the present invention in a portable computer, tablet, mobile phone, electric vehicle, or energy storage system. [Brief explanation of the drawing]

[0042] [Figure 1]This is an X-ray diffraction pattern of standard LaB6 material in the range of 40° to 70° (x-axis: 2θ (degrees), y-axis: intensity (arbitrary unit)). [Figure 2] This is the X-ray diffraction pattern of EX1.1 in the 42° to 47° range after separating the contributions of Kα1 and Kα2 (x-axis: 2θ (degrees), y-axis: intensity (arbitrary units)). [Figure 3] This is a cross-sectional EDS (CS-EDS) scan of EX1.1 showing the concentration gradients of Ni and Co from the periphery to the center of the secondary particles (x-axis: distance from the periphery (μm), y-axis: elemental concentration (mol%) relative to the total molar concentration of Ni, Mn, and Co). [Figure 4] This is a cross-sectional EDS (CS-EDS) scan of EX1.2 showing the concentration gradients of Ni and Co from the periphery to the center of the secondary particles (x-axis: distance from the periphery (μm), y-axis: elemental concentration (mol%) relative to the total molar concentration of Ni, Mn, and Co). [Figure 5] This is a cross-sectional EDS (CS-EDS) scan of CEX1, showing that there is no concentration gradient of Ni and Co from the edge to the center of the secondary particles (x-axis: distance from the edge (μm), y-axis: elemental concentration (mol%) relative to the total molar concentration of Ni, Mn, and Co). [Figure 6] This is a cross-sectional EDS (CS-EDS) scan of CEX2, showing that there is no concentration gradient of Ni and Co from the edge to the center of the secondary particles (x-axis: distance from the edge (μm), y-axis: elemental concentration (mol%) relative to the total molar concentration of Ni, Mn, and Co). [Modes for carrying out the invention]

[0043] The Ni-rich NMC cathode material according to the present invention typically exhibits improved first-cycle efficiency (E F), it has one or more advantages, such as cycle stability and thermal stability, which promote a higher level of safety. This is thought to be achieved by a cathode material in which there is a difference in cobalt and nickel concentrations between the center and the edge, with less Ni content at the edge than in the center, more Co content at the edge than in the center of the particle, and furthermore, the secondary particles of the cathode material have a specific average crystallite size.

[0044] Typically, the cathode material of the present invention comprises secondary particles having a median size D50 of at least 2 μm, preferably at least 3 μm, as determined by laser diffraction particle size analysis.

[0045] Preferably, this material has a median size D50 of secondary particles of up to 16 μm, preferably up to 15 μm, as determined by laser diffraction particle size analysis.

[0046] It is obvious that further embodiments of the product according to the present invention can be provided by combining the features covered by the various embodiments of the product described above.

[0047] In a further aspect of the present invention, the positive electrode material of the present invention is The first step is to co-precipitate the first metal source with a base to obtain the first M' system intermediate precursor. The first metal source is co-precipitated with a base, and the M'-system intermediate precursor seed of B1 is added to obtain the second M'-system intermediate precursor. A second metal source is precipitated on a second M'-system intermediate precursor using a base to obtain a third M'-system precursor having a difference in cobalt and nickel concentrations between the center and the periphery. The third M'-system precursor obtained, which has a difference in cobalt and nickel concentrations between the center and the periphery, is mixed with a lithium source to obtain a mixture, and The step of heating the mixture in an oxidizing atmosphere at a temperature of 650°C to less than 750°C to obtain lithium transition metal oxide powder. It can be prepared by a method including

[0048] In the final step of the method of the present invention, the advantage of using a specific heating temperature is that crystallite growth of secondary particles is prevented or limited, and the difference in cobalt and nickel concentrations between the center and edge of the precursor is reliably maintained in the cathode material.

[0049] Typically, the first metal source is a transition metal salt, preferably a sulfate of Ni, Mn, and / or Co, which is the M' element.

[0050] Typical bases used are alkali compounds, such as alkali hydroxides, such as sodium hydroxide, and / or ammonia.

[0051] Possible lithium sources include LiOH, Li2O, and / or LiOH.H2O.

[0052] The second metal source used to prepare the third M'-system precursor is typically a transition metal salt, preferably a sulfate of Mn and / or Co, which is the M' element.

[0053] Typically, the heating step is carried out over a period of 6 to 36 hours.

[0054] Optionally, element-containing compounds can be added to the cathode material. Preferably, the element-containing compound is added to the M'-type precursor, which has a difference in cobalt and nickel concentrations between the center and the periphery, in the step of mixing it with the lithium source. Alternatively, the element-containing compound may be mixed with the M'-type precursor, which has a difference in cobalt and nickel concentrations between the center and the periphery, before the mixing step.

[0055] Preferably, the elements of the elemental compound are elements other than Li, O, Ni, Co, Mn, and Al, and more preferably selected from the group consisting of B, Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, W, Zn, and Zr.

[0056] In addition, the method described above is A step of obtaining a mixture by mixing lithium transition metal oxide powder with a solution containing aluminum sulfate, wherein the solution contains S in an amount of 300 ppm to 3000 ppm relative to the weight of the dry powder. The step of heating the mixture in an oxidizing atmosphere at a temperature of 250°C to less than 500°C to obtain a positive electrode active material powder. It may include.

[0057] Preferably, the positive electrode active material contains S in an amount of 0.6 mol% to 3.0 mol% relative to M'.

[0058] In the following embodiments for carrying out the invention, preferred embodiments are described in detail to enable the implementation of the invention. Although the invention is described with reference to these particular preferred embodiments, it will be understood that the invention is not limited to these preferred embodiments. In contrast, the invention includes a number of substitutes, variations and equivalents, as will become apparent when considering the following embodiments for carrying out the invention.

[0059] Experimental tests used in the examples In this embodiment, the following analysis method is used.

[0060] A) Particle size distribution (PSD) analysis Here, the cathode active material powder examples described below are dispersed in an aqueous medium, and the PSD is measured using a Malvern Mastersizer 3000 equipped with a Hydro MV wet dispersion accessory. To improve the dispersion of the cathode active material powder examples, sufficient ultrasonic irradiation and stirring are applied, and an appropriate surfactant is introduced. D50 is defined herein as the particle size at 50% of the cumulative volume % distribution.

[0061] B) Inductively coupled plasma (ICP) analysis The positive electrode active material examples described below are measured by inductively coupled plasma (ICP) using an Agillent ICP 720-ES. Dissolve 1 gram of each example's powder sample in 50 mL of high-purity hydrochloric acid in an Erlenmeyer flask. Cover the flask with a watch glass and heat on a 380°C hot plate until the sample is completely dissolved. After cooling to room temperature, transfer the solution and rinse water from the Erlenmeyer flask to a 250 mL volumetric flask. Then, fill the volumetric flask to the 250 mL mark with DI water and then homogenize completely. Take an appropriate amount of solution with a pipette and transfer it to a 250 mL volumetric flask for a second dilution. Fill the volumetric flask to the 250 mL mark with the internal standard and 10% hydrochloric acid and then homogenize. Finally, this solution is used for ICP measurement. The measured content of Ni, Co, Mn, Al, and elements other than Li, Ni, Mn, Co, O, and Al (contents x, y, z, b, and a, respectively) is expressed as mol% of the total content of these elements.

[0062] C) Coin cell test For the preparation of the positive electrode in each of the examples described below, a slurry containing the examples of positive electrode active material described herein, a conductor (Super P, Timcal), and a binder (KF#9305, Kureha) (in a weight ratio of 90:5:5) is prepared in a solvent (NMP, Mitsubishi) using a high-speed homogenizer. The homogenized slurry is spread onto one side of an aluminum foil using a doctor blade coater with a 230 μm gap. The slurry-coated foil is dried in an oven at 120°C and then pressed using a calendering tool. It is then dried again in a vacuum oven to completely remove any residual solvent from the electrode film. The coin cell is assembled in a glove box filled with argon. A separator (Celgard 2320) is placed between the positive electrode and one piece of lithium foil to be used as the negative electrode. 1M LiPF6 in EC / DMC(1:2) 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.

[0063] Each cell is cycled at 25°C using a Toscat-3100 computer-controlled galvanostatic cycling station (Toyo). The coin cell test schedule used to evaluate the samples is detailed in Table 1. The schedule uses a 1C current definition of 160mA / g and includes evaluation of rate performance at 0.1C in the 4.3V to 3.0V / Li metal window range. The initial charge capacity (CQ1) and discharge capacity (DQ1) are measured in constant current mode (CC). The first cycle efficiency (E F ) is expressed as follows in %, %:

[0064]

number

[0065] [Table 1]

[0066] 4D) Cross-sectional energy dispersive X-ray spectroscopy (CS-EDS) D1) Cross section preparation The cross-sections of the positive electrode active material examples described below are prepared using the ion beam cross-section polishing (CP) instrument JEOL (IB-0920CP). This instrument uses argon gas as the beam source.

[0067] To prepare the test specimen, a small amount of positive electrode active material powder is mixed with resin and curing agent, and the mixture is then heated on a hot plate for 10 minutes. After heating, it is placed in an ion beam instrument for cutting, and the settings are adjusted to the standard procedure of a voltage of 6.5kV for a duration of 3 hours.

[0068] D2) Energy-dispersive X-ray spectroscopy (EDS) analysis Using the examples of positive electrode active materials prepared according to method D1) above, the concentrations of Ni, Mn, and Co from the edge to the center of the positive electrode material secondary particles are analyzed by energy-dispersive X-ray spectroscopy (EDS). For the analysis of each example, secondary particles with a diameter around the D50 value are selected by measurement using a PSD according to section A). The EDS is a 50 mm Oxford Instruments machine. 2 The analysis is performed using a JEOL JSM 7100F SEM facility equipped with an X-MaxN EDS sensor. EDS analysis of cathode active material secondary particles provides quantitative elemental analysis of the cross-section, assuming the particles are spherical. A straight line is set from the edge to the center of the secondary particle, and multiple points are set along the line, with a distance of approximately 0.4 μm between each point. Ni, Mn, and Co concentrations are measured at all points and expressed as mol% relative to the sum of Ni, Mn, and Co content at each point.

[0069] E) X-ray powder diffraction (XRD) E1)XRD measurement The X-ray diffraction patterns of the cathode active material powder examples described below were collected using a Rigaku Ultima 4 X-ray diffractometer with a Cu Kα radiation source (40kV, 40mA) emitting at a wavelength of 1.5418 Å. The instrument configuration consisted of a 1° solar slit (SS), a 10mm divergent height limiting slit (DHLS), a 1° divergence slit (DS), and a 0.3mm reception slit (RS). The goniometer diameter was 185mm. In XRD, the diffraction patterns were obtained in the range of 40-80° (2θ) with a scan rate of 1° / min and a step size of 0.02° / scan.

[0070] E2) Crystallite size calculation The average crystallite size is determined by XRD measurements of the positive electrode active material secondary particles. The average crystallite size has a good correlation with the average primary particle size of the positive electrode active material secondary particles. Therefore, the average crystallite size obtained by XRD is often used as a relative parameter for estimating the primary particle size of the secondary particles.

[0071] The average crystallite size of the secondary particles in the positive electrode active material examples described below is determined according to the following steps.

[0072] Step 1) Collect diffraction patterns of standard LaB6 material (99.5%, Alfa Aesar, manufactured by Fisher Scientific, e.g., https: / / www.fishersci.fi / shop / products / lanthanum-boride-99-5-reo / 11373888) by XRD measurement as described in E1.

[0073] Step 2) Collect the diffraction pattern of the positive electrode active material by XRD measurement as described in E1.

[0074] Step 3) Peak integration is performed for LaB6 from 2θ between 48° and 50°, and for the positive electrode active material from 2θ between 43° and 46°. Peak integration is performed in Origin 2018b Version b9.5.5.409, and the baseline is set to an endpoint weighted to 10%. From this step, the integrated peak areas of LaB6 and the positive electrode active material are obtained, and A LaB6 and A active material Let's call it that.

[0075] Step 4) Perform fitting to separate the contributions of Kα1 and Kα2. Fitting is performed on the diffraction pattern of LaB6 collected (from Step 1) and the diffraction pattern of the cathode active material (from Step 2). Fitting can be performed with any graphing and analysis software, provided that the computational constraints described in the calculation method can be implemented. In this invention, fitting is assisted by the solver tool built into Microsoft Excel software version 2008. The tool is used to fit the peak function based on several predefined conditions and objectives. The predefined conditions include the fitting function, constraints, and input value table, and the objective is a cell containing the SUMXMY2 equation. Each predefined condition and objective is described below.

[0076] - Fitting function The fitting function is a pseudo-Voigt equation, that is, a linear equation that combines Gaussian and Lorentz functions. The equation is as follows:

[0077]

number

[0078] y o = offset, x c = center position of the peak, A = peak area, w = peak width (full width at half maximum), and m u =Profile shape coefficient. These five parameters are variable cells set in the Solver tool.

[0079] - restraint Several related constraints are specified in the following calculations. The peak widths of Kα1 and Kα2 are, Kα1 ≤0.4°, w Kα2 ≤0.4°, and w Kα1 =w Kα2 Therefore, the ratio of the integral areas between Kα1 and Kα2 is A Kα2 ≤A Kα1 *It is 0.5. The Kα1 and Kα2 peak positions are Xc Kα1 =Xc Kα2 -d, where d can be calculated using the Rachinger equation (Schramm, RE, Correction and calculations on an X-ray diffraction line profile: A computer program, National Bureau of Standards, 1971, pp. 8-9):

[0080]

number

[0081] In the equation, λ is the wavelength of Cu Kα = 1.54178 Å, λ1 is the wavelength of Cu Kα1 = 1.54051 Å, and λ2 is the wavelength of Cu Kα2 = 1.54433 Å (Nicol, AW, Physicochemical methods of mineral analysis, Plenum Press, New York, 1975, p.254), and θ is half the center point of the 2θ range selected in step 3 (θ for LaB6 is 49° / 2 = 24.5°, and θ for the active material is 44.5° / 2 = 22.25°). Therefore, the value of d is 0.129° for LaB6 and 0.116° for the positive electrode active material.

[0082] - Input Value Table An input value table is a set of initial data used as a starter to improve fitting and obtain repeatable results. This involves predicting parameter values ​​based on estimations. Table 2.1 shows an example input value table for EX1.1, an example of a cathode material according to the present invention.

[0083] [Table 2]

[0084] In the calculation, the input data is linearly baselined to 0, so the y0 offset is always 0. The peak positions are systematically determined, and at 2θ, Kα1 is placed lower than Kα2. u and w are set to 0.5 and 0.2, respectively. The XRD peak area in the 42° to 47° range is assumed to be triangular, formed using a base of 1.5° and the maximum peak intensity from the baseline as the height of the triangle. The Kα1 area is 2 / 3 of the calculated total XRD peak area, and the Kα2 area is 1 / 3 of the calculated total XRD peak area.

[0085] -the purpose The objective of the solver calculation is to set the minimum value of SUMXMY2. This function returns the sum of the squared differences between two array values. In this case, the difference is between the true value and the calculated value. Goodness of fit R 2 The calculation terminates when the result reaches 99.5% or higher. Otherwise, the iteration continues until the target minimum value is reached.

[0086] The diffraction pattern of LaB6 is shown in Figure 1. An example of the XRD peak of EX1.1 after the fitting process is shown in Figure 2 (x-axis: 2θ, y-axis: intensity). The results of the calculated parameters are shown in Table 2.2.

[0087] [Table 3]

[0088] From this step, the maximum intensity of the Kα1 peak was obtained for each of LaB6 and the positive electrode active material, and each was I LaB6 and I active material Let's call it that.

[0089] Step 5) Calculate the integral width using the following formula.

[0090]

number

[0091] From this step, the integral widths of LaB6 and the positive electrode active material are obtained, respectively, IB LaB6 and IB active material Let's call it that.

[0092] Step 6) The IB of the positive electrode active material is corrected for the spread originating from the equipment using the following formula.

[0093]

number

[0094] In the formula, β is the corrected IB active matetrial That is the case.

[0095] Step 7) Scherrer method:

[0096]

number

[0097] [In the formula, τ is the average crystallite size (nm) calculated from XRD, λ is the X-ray wavelength (nm), K is the Scherrer constant set to 0.9, and θ is the x of Kα1 of the positive electrode active material obtained from step 4] c (in radians), and β is the corrected IB obtained from step 6). active material The average crystallite size of the secondary particles of the positive electrode active material is calculated by using [this method].

[0098] [Examples] The present invention will be further explained in the following examples.

[0099] [Example 1] EX1.1 is an example of a cathode material according to the present invention, prepared by a solid-phase reaction between a lithium source and a transition metal source precursor A, in order to prepare the cathode material according to the present invention by the following method steps. 1) Preparation of Precursor A: The precipitation process of Precursor A was carried out in a reactor with a liquid volume of 10 L using an overflow pipe and a 400 W impeller motor. An impeller with a diameter of 10 cm was stirred at 800 RPM. The reactor had four baffles that enabled intense stirring. To avoid oxidation caused by intense stirring, a nitrogen gas flow of 50 L / h was applied above the liquid level. After preparing three solutions containing nickel sulfate, manganese sulfate, and cobalt sulfate (NiSO4, MnSO4, CoSO4), each having a total metal concentration of 110 g / L, and then mixing them, a first solution with a Ni:Mn:Co molar ratio of 87:5:8 was obtained. By mixing two solutions containing manganese sulfate and cobalt sulfate (MnSO4 and CoSO4), each having a total metal concentration of 110 g / L, a second solution with a Ni:Mn:Co molar ratio of 0:5:95 was prepared. A 400 g / L NaOH solution and a 25% undiluted ammonia solution were used. The total metal composition of Precursor A prepared in Processes S1 to S3 was Ni 0.85 Mn 0.05 Co 0.10 as follows.

[0100] a. Preparation of the First M’-Based Intermediate Precursor in S1: Ni 0.87 Mn 0.05 Co 0.08 (OH)2 The first intermediate precursor was prepared using typical co-precipitation in a continuous stirred tank reactor (CSTR) with a residence time of 6 hours. At the start, the reactor was filled with water and ammonia to obtain an ammonia solution with a concentration of 15 g / L inside. The temperature inside the reactor was 60 °C. After filling the reactor with the starting solution, different reagents (the first solution, NaOH solution, NH3 solution) were simultaneously pumped into the reactor at different injection points while maintaining the ratio of ammonia to metal at 1:1 and keeping the pH around 11.7. During the precipitation reaction, more than 2 OH -Ions should be present. After 24 hours, the reactor was in a steady state, the D50 was 5 μm to 20 μm, and the slurry was collected from the overflow. The precipitated metal hydroxide was washed and filtered under a protective atmosphere to remove dissolved salts and ammonia. 200 grams of wet cake was repulped in 1 L of water and treated with mechanical grinding using a ball mill. This treatment reduced the D50 size to less than 2 μm, as determined by PSD analysis.

[0101] b. Preparation of the second M' system intermediate precursor of S2: Ni 0.87 Mn 0.05 Co 0.08 The (OH)2 second intermediate precursor was prepared using a modified coprecipitation in a continuous stirred tank reactor (CSTR) with an intrinsic or mean residence time of 3 hours. The first solution composition of MeSO4 was used. At the start, the reactor was filled with water and ammonia to obtain a 15 g / L ammonia solution inside. The temperature inside the reactor was 60°C. After filling the reactor with the starting solution, different reagents (first solution, NaOH solution, NH3 solution) were pumped into the reactor simultaneously at different injection points, while maintaining an ammonia-to-metal ratio of 1:1 and keeping the pH around 11.7 with NaOH solution. Typically, more than two OH groups were present for each metal ion in the solution. - Ions should be present. After 6 hours, the first intermediate precursor from 100 grams of S1 was added to the reactor. After at least 6 hours, the particles had grown to approximately 6 μm to 11 μm. At this point, the overflow slurry was collected in a 3 L beaker, and the particles were allowed to settle in the beaker. The beaker was decanted every 30 minutes, and the slurry was returned to the reactor. When the particles reached a sufficient size (determined by PSD analysis, with a D50 of approximately 11 μm), the dosing of the reagent was stopped.

[0102] c.S3 Preparation of the third M' system precursor: Dosing of all reagents (second solution, NaOH solution, NH3 solution) to the CSTR was resumed, and the overflow was collected in a 3L beaker. The beaker was decanted every 30 minutes to remove the filtrate, and the slurry was returned to the reactor. This procedure was continued for 50 minutes. The precipitated metal (oxy) hydroxide was washed and filtered under a protective atmosphere to remove dissolved salts and ammonia. The wet cake was dried in an oven at 150°C under nitrogen. The mean metal composition of precursor A, determined by ICP analysis, was Ni:Mn:Co = 85:5:10 (mol%). To maintain a constant final product composition, important factors such as pH, stirring rate, chemical concentration, and temperature were precisely controlled during the precipitation process.

[0103] 2) Mixing: Precursor A prepared in step 1) was mixed with LiOH in an industrial blender at a Li-to-metal molar ratio of 1.02 (Li / Me; where Me is the sum of Ni, Mn, and Co).

[0104] 3) Heating: The mixture obtained from step 2) was heated at 690°C for 12 hours under an oxygen atmosphere, then pulverized and sieved to obtain a positive electrode material of EX1.1 with a composition of Ni:Mn:Co = 86:4:10 (in mol%) determined by ICP analysis and a D50 of approximately 11 μm determined by PSD analysis.

[0105] EX1.2 is an example of the cathode material according to the present invention, prepared by the same method as EX1.1, except that the heating temperature in heating step 3) was 715°C. EX1.2 was determined by ICP analysis to have a composition of Ni:Mn:Co = 86:4:10 (in mol%) and by PSD analysis to have a D50 of approximately 11 μm.

[0106] Comparative Example 1 CEX1 is a comparative example of a positive electrode material prepared by the same method as EX1.1, except that the heating temperature used in the heating step 3) was 760°C. CEX1 had a composition of Ni:Mn:Co = 86:4:10 (in mol%) determined by ICP analysis and a D50 of around 11 μm determined by PSD analysis.

[0107] Comparative Example 2 CEX2 is a comparative example of a positive electrode material obtained through a solid-state reaction between a lithium source and a transition metal-based source precursor B in the following method steps. 1) Preparation of precursor B: Precursor B had a molar ratio of Ni:Mn:Co of 85:5:10 in the first solution used in S1 and S2, and was prepared by the same method as precursor A of EX1.1, except that step 1) c) S3 was omitted. The total metal composition of precursor B was Ni 0.85 Mn 0.05 Co 0.10 and it was. 2) Mixing: The precursor B prepared from step 1) was mixed with LiOH in an industrial blender at a mol ratio of Li to metal (Li / Me) of 1.02. 3) Heating: The mixture obtained from step 2) was heated at 715°C for 12 hours in an oxygen atmosphere, followed by pulverization and sieving to obtain CEX2 having a composition of Ni:Mn:Co = 85:5:10 (in mol%) determined by ICP analysis and a D50 of around 11 μm determined by PSD analysis.

[0108] [Example 2] EX2 is an example of a positive electrode material according to the present invention prepared through the following method steps. 1) Preparation of aluminum sulfate solution: 7.01 grams of Al2(SO4)3·16H2O powder is mixed with 30 grams of deionized water. 2) Mixing: 1 kg of EX1.1 is mixed with the aluminum sulfate solution prepared in step 1) to obtain a wet mixture. 3) Heating: The mixture obtained from step 2) was heated at 385°C for 8 hours under an oxygen atmosphere, then ground and sieved to obtain EX2. EX2 was determined by ICP to have a composition of Ni:Mn:Co = 85:5:10 (in mol%) and by PSD analysis to have a D50 of approximately 11 μm. Furthermore, EX2 was determined by ICP to contain 1.09 mol% S and 0.37 mol% Al relative to M'.

[0109] result The results of the experimental tests used in the examples described above are as follows:

[0110] [Table 4]

[0111] Table 3 summarizes the ICP values ​​of S and Al, average crystallite size, and electrochemical properties of EX1.1, EX1.2, CEX1, CEX2, and EX2. The positive electrode active materials EX1.1 and EX1.2, prepared from precursor A and fired at temperatures of 680°C to 750°C, showed the highest DQ1 and E F It was demonstrated that this is the case. Low E F The advantage in the value was also related to the fact that the average crystallite size of the secondary particles, calculated by the XRD method in Section E), was less than 40 nm. At firing temperatures higher than 750°C, it was found to be disadvantageous because it accelerates the growth of the average crystallite size of the secondary particles to values ​​exceeding 40 nm, as shown in Table 3 for CEX1.

[0112] EX2 was obtained by mixing EX1.1 with Al2(SO4)3 and then heating at 385°C. This process yielded DQ1 and E F This represents a further improvement compared to EX1.1, and it indicates that the presence of both Al and S in the positive electrode active material of EX2 is beneficial to its electrochemical properties.

[0113] EX1.2, prepared from precursor A and lithium-ionized at 715°C, has higher DQ1 and E than CEX2, which was prepared from precursor B at the same calcination temperature. F The values ​​are shown. From Table 3, it can be concluded that precursors with concentration gradient characteristics are preferable for preparing cathode active materials with improved electrochemical properties.

[0114] Figures 3-6 show the CS-EDS analyses described in Section D) for EX1.1, EX1.2, CEX1, and CEX2, respectively. The analysis is performed to investigate the concentration differences of cobalt and nickel between the center and the periphery of the positive electrode active material. For each of these examples, the mol% of Ni, Mn, and Co at the periphery and center of the secondary particles are shown in Table 4. EX1.1, manufactured at 690°C, showed Ni and Co gradients from the periphery to the center of the positive electrode active material secondary particles. Ni and Co concentration gradients were observed from the periphery (0 μm) to the center of EX1.1, with the Ni concentration at the periphery being lower than that at the center. Conversely, the Co concentration at the periphery of EX1.1 was higher than that at the center, following the composition of precursor A. On the other hand, in CEX1 prepared at a higher lithiumization temperature of 760°C, no concentration gradients for Ni or Co were observed, indicating that when the calcination temperature was higher than 750°C, the difference in cobalt and nickel concentrations between the center and edge of the precursor disappeared. As a result, CEX2 was produced from precursor B, which also did not show Ni and Co concentration gradients.

[0115] [Table 5]

[0116]

number

[0117] A positive electrode active material having an average crystallite size of less than 40 nm and a concentration gradient characteristic indicated by the change in Ni and Co concentrations from the periphery to the center of the secondary particles exhibits an initial discharge capacity (DQ1) higher than 205 mAh / g and an initial cycle efficiency (E) higher than 90%. F The objective of this invention, which is to provide a positive electrode active material having ), can be achieved.

Claims

1. A positive electrode active material suitable for lithium-ion rechargeable batteries, comprising Li, M', and oxygen, wherein M' is Ni with a content of x between 75.0 mol% and 95.0 mol% relative to M', Co with a content of y ranging from 1.0 mol% to 25.0 mol% relative to M', Mn with a content z of 0.0 mol% or more and 25.0 mol% or less relative to M', Al content of b is 0.1 mol% to 5.0 mol% relative to M'. S with a content of 0.01 mol% to 5.0 mol% relative to M' Includes, The contents x, y, z, a, and b were measured by ICP. x + y + z + a + b is 100.0 mol%, The positive electrode active material includes secondary particles comprising a plurality of primary particles, The Ni content of the positive electrode active material is measured by cross-sectional EDS (CS-EDS) at the edge of the secondary particles of the positive electrode active material. ｅｄｇｅ and Co content Co ｅｄｇｅ The Ni and Co content is expressed as mol% of the sum of the Ni, Mn, and Co content, as measured by CS-EDS at the edge of the secondary particles of the positive electrode active material. The Ni content of the positive electrode active material is measured by CS-EDS at the center of the secondary particles of the positive electrode active material. ｃｅｎｔｅｒ and Co content Co ｃｅｎｔｅｒ The Ni and Co content is expressed as mol% of the sum of the Ni, Mn, and Co content, as measured by CS-EDS at the center of the secondary particles of the positive electrode active material. Ni ratio ｅｄｇｅ / Ni ｃｅｎｔｅｒ < 0.98, ratio Co ｅｄｇｅ / Co ｃｅｎｔｅｒ > 1.10, The secondary particles are determined by XRD to have an average crystallite size of at least 15 nm and a maximum of 40 nm. Cathode active material.

2. The positive electrode active material according to claim 1, wherein Al has an content b of 0.1 mol% to 3.0 mol% relative to M'.

3. Ni ｅｄｇｅ / Ni ｃｅｎｔｅｒ <0.97 and Co ｅｄｇｅ / Co ｃｅｎｔｅｒ >1.15, the positive electrode active material according to claim 1.

4. Ni ｅｄｇｅ / Ni ｃｅｎｔｅｒ ≤ 0.96 and Co ｅｄｇｅ / Co ｃｅｎｔｅｒ The positive electrode active material according to claim 1, wherein the ratio is ≥ 1.

30.

5. Determined by CS-EDS analysis, Ni ｅｄｇｅ and Ni ｃｅｎｔｅｒ The difference between and is at least 5 mol%, Co ｅｄｇｅ and Co ｃｅｎｔｅｒ The positive electrode active material according to claim 1, wherein the difference between it and is at least 2 mol%.

6. The Mn content of the positive electrode active material is measured by cross-sectional EDS (CS-EDS) at the edge of the secondary particles. ｅｄｇｅ The Mn content is expressed as mol% relative to the sum of the Ni, Mn, and Co content, as measured by CS-EDS at the edge of the secondary particles of the positive electrode active material. Mn ｅｄｇｅ It is greater than 0 mol%, The positive electrode active material according to claim 1.

7. The positive electrode active material according to claim 1, wherein the Ni content x is ≥ 77.0 mol% relative to M'.

8. The positive electrode active material according to claim 1, wherein the Ni content x is ≤ 93.0 mol% relative to M'.

9. The positive electrode active material according to claim 1, wherein the Co content is 3 mol% ≤ y ≤ 20 mol% relative to M'.

10. The positive electrode active material according to claim 1, wherein a is 0.1 mol% to 4 mol% with respect to M'.

11. ratio Co ｅｄｇｅ / Co ３／４ However, relative Co ｅｄｇｅ / Co ｃｅｎｔｅｒ Smaller, here, Co ３／４ The positive electrode active material according to claim 1, wherein the Co content is expressed as mol% of the sum of the Ni, Mn, and Co content, as measured by CS-EDS at 3 / 4 of the distance from the edge of the secondary particle to the center of the secondary particle.

12. Ni ratio ｅｄｇｅ / Ni ３／４ However, ratio Ni ｅｄｇｅ / Ni ｃｅｎｔｅｒ Larger, here, Ni ３／４ The positive electrode active material according to claim 1, wherein the Ni content is expressed as mol% of the sum of the Ni, Mn, and Co content, as measured by CS-EDS at 3 / 4 of the distance from the edge of the secondary particle to the center of the secondary particle.

13. 0.2 ≤ cobalt gradient (mol% / μm) ≤ 1.0, and the cobalt gradient is given by the following equation: [Math 1] The positive electrode active material according to claim 1, as represented by...

14. A method for manufacturing a positive electrode active material, The positive electrode active material is a positive electrode active material suitable for lithium-ion rechargeable batteries, and contains Li, M' and oxygen, wherein M' is Ni with a content of x between 75.0 mol% and 95.0 mol% relative to M', Co with a content of y ranging from 1.0 mol% to 25.0 mol% relative to M', Mn with a content z of 0.0 mol% or more and 25.0 mol% or less relative to M', Al content of b is 0.0 mol% to 5.0 mol% relative to M'. Elements other than Li, Ni, Mn, Co, O, and Al, present in a content a of 0.0 mol% to 5.0 mol% relative to M'. Includes, The contents x, y, z, a, and b were measured by ICP. x + y + z + a + b is 100.0 mol%, The positive electrode active material includes secondary particles comprising a plurality of primary particles, The Ni content of the positive electrode active material is measured by cross-sectional EDS (CS-EDS) at the edge of the secondary particles of the positive electrode active material. ｅｄｇｅ and Co content Co ｅｄｇｅ The Ni and Co content is expressed as mol% of the sum of the Ni, Mn, and Co content, as measured by CS-EDS at the edge of the secondary particles of the positive electrode active material. The Ni content of the positive electrode active material is measured by CS-EDS at the center of the secondary particles of the positive electrode active material. ｃｅｎｔｅｒ and Co content Co ｃｅｎｔｅｒ The Ni and Co content is expressed as mol% of the sum of the Ni, Mn, and Co content, as measured by CS-EDS at the center of the secondary particles of the positive electrode active material. Ni ratio ｅｄｇｅ / Ni ｃｅｎｔｅｒ < 0.98, ratio Co ｅｄｇｅ / Co ｃｅｎｔｅｒ > 1.10, The secondary particles are determined by XRD to have an average crystallite size of at least 15 nm and a maximum of 40 nm. It is a positive electrode active material, The following are the sequential steps: The first step is to co-precipitate the first metal source with a base to obtain the first M' system intermediate precursor. The first metal source is co-precipitated with a base, and then the first M'-system intermediate precursor is added to obtain a second M'-system intermediate precursor. A second metal source is precipitated on the second M'-system intermediate precursor using a base to obtain a third M'-system precursor having a difference in cobalt and nickel concentrations between the center and the periphery. The third M'-system precursor obtained, which has a difference in cobalt and nickel concentrations between the center and the periphery, is mixed with a lithium source to obtain a mixture, and The step of heating the mixture in an oxidizing atmosphere at a temperature of 650°C to 750°C to obtain lithium transition metal oxide powder. A method that includes this.

15. A battery comprising the positive electrode active material according to any one of claims 1 to 13.

16. Use of the battery according to claim 15 in a portable computer, tablet, mobile phone, electric vehicle, or energy storage system.

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