Positive electrode active material powder and method for manufacturing positive electrode active material powder

Abstract

The present invention relates to a positive electrode active material powder comprising secondary particles comprising a plurality of primary particles, in which the positive electrode active material powder comprises a lithium metal oxide comprising lithium (Li), M'and oxygen (O), in which the first lithium metal oxide has a layered [alpha]-NaFeO2 structure; wherein M'comprises titanium (Ti) and at least one element selected from the group consisting of nickel (Ni) and manganese (Mn); wherein there is a grain boundary between adjacent ones of the secondary particles; wherein the Ti concentration in the grain boundary is greater than the Ti concentration in the adjacent primary particles; and wherein the positive electrode active material powder has a surface area of between 0.3 m2 / g and 1.2 m2 / g, as determined by BET measurement.

Description

[0001] TECHNICAL FIELD AND BACKGROUND The present invention relates to a positive electrode active material powder comprising secondary particles containing a plurality of primary particles, wherein the positive electrode active material powder comprises a first lithium metal oxide having a layered α-NaFe02 structure.

[0002] Lithium transition metal oxides having a layered α-NaFe02 structure have a cation mixing between lithium (Li) and transition metals, and an increase in the cation mixing leads to a problem of low initial discharge capacity caused by hindering diffusion of Li ions.

[0003] Therefore, it is required that the positive electrode active material powder having a layered α-NaFe02 structure should exhibit excellent electrochemical properties such as high initial discharge capacity.

[0004] A first object of the present invention is to provide a positive electrode active material powder capable of solving the above-mentioned problems. Specifically, the first object is achieved by providing a positive electrode active material powder comprising a first lithium metal oxide having a layered α-NaFe02 structure, wherein a concentration of titanium (Ti) present in a grain boundary between two adjacent primary particles of the secondary particles is greater than a concentration of Ti in the adjacent primary particles, and wherein the positive electrode active material powder has a specific surface area of 0.5 m2 / g to 1.2 m2 / g, as determined by BET measurement. 2 2 / g to 1.2 m2 / g, as determined by BET measurement.

[0005] A second object of the present invention is to provide a method for manufacturing the positive electrode active material powder according to the present invention.

[0006] A third object of the present invention is to provide a battery comprising the positive electrode active material powder according to the present invention.

[0007] A fourth object of the present invention is to provide a use of the battery according to the present invention. SUMMARY

[0008] The first object is achieved by providing a positive electrode active material powder suitable for use in a lithium-ion rechargeable battery, the positive electrode active material powder comprising secondary particles containing a plurality of primary particles, wherein the positive electrode active material powder comprises a first lithium metal oxide containing Li, M' and oxygen (O), wherein the first lithium metal oxide has a layered α-NaFe02 structure; wherein M' comprises Ti and at least one element selected from the group consisting of nickel (Ni) and manganese (Mn); wherein a grain boundary is present between adjacent primary particles of the secondary particles; ​The Ti concentration at the grain boundaries is greater than the Ti concentration in adjacent primary particles; and The positive electrode active material powder has a particle size of 0.5 μm. 2 / g and 1.2 m 2 Surface area between / g, as determined by BET measurement.

[0009] The second objective is achieved by providing a method for manufacturing a positive electrode active material powder according to the present invention, wherein the method comprises the following sequential steps: -Step 1) Mix a second lithium metal oxide containing Li, M' and O with an aqueous solution to obtain a slurry, filter, and then dry the slurry to obtain a dry powder. -Step 2) Mix the dried powder with a Ti-containing compound, preferably TiO2, wherein the compound contains Ti in an amount between 300 ppm and 4000 ppm by weight relative to the dried powder, and - Step 3) Heat the mixture in an oxidizing atmosphere at a temperature between 450°C and 650°C to obtain the positive electrode active material powder.

[0010] The third objective is achieved by a battery comprising a positive electrode active material powder according to the invention.

[0011] The fourth objective is achieved by the use of the battery according to the invention in an electric vehicle or a hybrid electric vehicle.

[0012] The positive electrode active material powder according to the present invention has excellent electrochemical properties, such as high initial discharge capacity (DQ1), low irreversible capacity (Qirr) and low capacity decay (QF). Attached Figure Description

[0013] Figure 1a This is a cross-sectional STEM image of EX2 at the first location.

[0014] Figure 1b yes Figure 1a EDS-mapped scan images.

[0015] Figure 1c It comes from Ru Figure 1b The line scan curve of Ti at the position indicated by the arrow in the figure.

[0016] Figure 2a This is a cross-sectional STEM image of EX2 at the second location. Figure 2b yes Figure 2a EDS-mapped scan images.

[0017] Figure 2c It comes from RuFigure 2b The line scan curve of Ti at the position indicated by the arrow in the figure. Detailed Implementation

[0018] In the following detailed description, preferred embodiments are described in detail to enable the practice of the invention. Although the invention has been described with reference to these specific preferred embodiments, it should be understood that the invention is not limited to these preferred embodiments. Rather, the invention includes numerous alternatives, modifications, and equivalents, as will become apparent from consideration of the following detailed description.

[0019] As used in this article, the range of values ​​for “from X to Y” includes the endpoints X and Y.

[0020] Positive electrode active material powder In a first aspect, the present invention relates to a positive electrode active material powder suitable for lithium-ion rechargeable batteries, comprising secondary particles containing a plurality of primary particles. The positive electrode active material powder contains a first lithium metal oxide containing Li, M' and O, wherein the first lithium metal oxide has a layered α-NaFeO2 structure. Wherein M' contains Ti and at least one element selected from the group consisting of Ni and Mn; There are grain boundaries between adjacent primary particles in the secondary particles; The Ti concentration at the grain boundaries is greater than the Ti concentration in adjacent primary particles; and The positive electrode active material powder has a particle size of 0.5 μm. 2 / g and 1.2 m 2 Surface area between / g, as determined by BET measurement.

[0021] The grain boundary is in a primary grain ( That is On the surface of microcrystals. Therefore, the shape of a grain boundary is defined by the shape of the primary grains adjacent to the grain boundary, and may approximate a straight shape, such as a polygon, when viewed in cross-section.

[0022] The size of the grain boundary is not particularly limited. When viewed in cross-section, the length and width of the grain boundary can each independently be about 50 to about 1000 nm, preferably about 60 to about 900 nm, and more preferably about 70 to about 800 nm. The length and width of the grain boundary can be perpendicular to each other and can be parallel to the surface of adjacent crystallites. The thickness of the grain boundary can be about 5 to about 100 nm, preferably about 10 to about 80 nm, and more preferably about 20 to about 50 nm. The thickness of the grain boundary can be perpendicular to the length and width of the grain boundary and can be perpendicular to the surface of adjacent crystallites. The thickness of the grain boundary is defined by the Ti concentration distribution obtained by line scanning through the grain boundary. The Ti concentration curve can be obtained by STEM-EDS measurement as described in this specification. Specifically, the Ti concentration curve obtained by STEM-EDS during line scanning through the grain boundary has a maximum value between the right and left points. The right-hand point corresponds to the first occurrence from the point of maximum value on the right, where the Ti concentration reaches the average Ti concentration of the positive electrode active material powder obtained by inductively coupled plasma-optical emission analysis (ICP-OES) as described in this specification. The left-hand point corresponds to the first occurrence from the point of maximum value on the left, where the Ti concentration reaches the average Ti concentration of the positive electrode active material powder obtained by ICP-OES. The grain boundary thickness is the distance from the right-hand point to the left-hand point.

[0023] The ratio of the maximum Ti concentration at the grain boundary to the Ti concentration obtained by ICP-OES relative to M' can be 5 or greater, preferably 7 or greater, more preferably 9 or greater, and even more preferably 11 or greater. This ratio can be 50 or less, preferably 40 or less, more preferably 30 or less, and even more preferably 25 or less. Specifically, the ratio can be from 5 to 50, preferably 7 to 40, more preferably 9 to 30, and even more preferably 11 to 25. If the ratio is less than 5, Ti enrichment may be insufficient to improve the electrochemical performance of the battery. If the ratio is greater than 50, the mechanical stability at the grain boundary may deteriorate.

[0024] The first lithium metal oxide containing Li, M', and O has a layered α-NaFeO2 structure. In the layered α-NaFeO2 structure, hexagonal metal oxide layers are separated by planes of alkali metals. The metal oxide layers form metal-centric oxygen octahedra separated by alkali metal ions, and the metal oxide layers are laterally offset to provide a three-layer structure. In this structure, alkali metal atoms occupy the so-called "3a" sites (x=0, y=0, and z=0), metal atoms occupy "3b" sites (x=0, y=0, and z=0.5), and oxygen atoms occupy "6c" sites (x=0, y=0, and z=0.25). Atomic coordinates and cell parameters can vary depending on the metal composition.

[0025] M' in the first lithium metal oxide contains Ti and at least one element selected from the group consisting of Ni and Mn. The Ti concentration at the grain boundaries is greater than the Ti concentration in the primary particles. Ti can concentrate at the grain boundaries, and therefore, Ti can be almost absent in the primary particles. Furthermore, the Ti concentration can exhibit a gradient, wherein the Ti concentration gradually decreases from the grain boundaries between primary particles toward the center of the primary particles. The Ti concentration at the grain boundaries can be measured by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) as described in this specification.

[0026] The positive electrode active material powder according to the present invention has a particle size of 0.3 μm. 2 / g or greater, preferably 0.4 m 2 / g or greater, more preferably 0.5 m 2 / g or greater, and more preferably 0.6 m 2 The surface area is 2.0 m² or greater, as determined by BET measurements as described in this specification. The positive electrode active material powder according to the invention has a surface area of ​​2.0 m². 2 / g or less, preferably 1.5m 2 / g or less, more preferably 1.2 m 2 / g or less, and more preferably 1.1 m 2 A surface area of ​​0.3 m² or less, as determined by BET measurements as described in this specification. Specifically, the positive electrode active material powder according to the invention has a surface area of ​​0.3 m² or less. 2 / g and 1.2 m 2 Between / g, preferably between 0.4 m 2 / g and 1.2 m 2 / g, more preferably between 0.5 m 2 / g and 1.2 m 2 Between / g, and more preferably between 0.6 m 2 / g and 1.1 m 2 The surface area between / g, as determined by BET measurements as described in this specification. As the surface area of ​​the positive electrode active material powder increases, the area of ​​regions where side reactions may occur also increases. These side reactions can cause phase transitions that alter the crystal structure of the lithium composite oxide constituting the positive electrode active material powder. This phase transition in the crystal structure of the positive electrode active material powder surface is one of the reasons for the reduced electrochemical characteristics (such as lifetime) of lithium secondary batteries.

[0027] The inventors of this invention have discovered that Ti enrichment in grain boundaries and the surface area of ​​the positive electrode active material powder are 0.5 m². 2 / g to 1.2 m2 The combination of / g results in excellent electrochemical properties of the battery. Specifically, the positive electrode active material powder according to the present invention exhibits high initial discharge capacity (DQ1), low irreversible capacity (Qirr), and low capacity decay (QF). Specifically, residual Li such as Li2CO3 and LiOH on the surface of the positive electrode active material can transform to form the cathode electrolyte interface (CEI), and thus increase the interfacial resistance. Furthermore, residual Li may decompose to produce gas, which may lead to surface degradation of the positive electrode active material. To remove residual Li, the surface of the positive electrode active material can be washed with an aqueous solution, but the surface area of ​​the positive electrode active material may increase due to washing. Without being bound by any theory, Ti enrichment at grain boundaries can offset the electrochemical performance degradation of the positive electrode active material caused by the increase in surface area after washing to remove residual Li.

[0028] In a preferred embodiment, M' comprises: - Ni with a content of x relative to M', where 70.0 at% ≤ x < 100.0 at% - Mn with a content of y relative to M', where 0.0 at% ≤ y ≤ 11.0 at%. -Co with a content of z relative to M', where 0.0 at% ≤ z ≤ 11.0 at%. - Ti with a content of a relative to M', where 0.0 at% -Al content b relative to M', where 0.0 at% ≤ b ≤ 2.0 at%. - Zr with a content of c relative to M', where 0.0 at% ≤ c ≤ 2.0 at%. - D with a content of d relative to M', wherein 0.0 at% ≤ d ≤ 2.0 at%, and D is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, La, Mg, Mo, Nb, S, Sr, V, W, Y and Zn; -Where x, y, z, a, b, c, and d are measured by ICP-OES; and -where x+y+z+a+b+c+d is 100.0 at.

[0029] As the Ni content in the first lithium metal oxide increases, the amount of Li byproducts present on the surface of the positive electrode active material powder increases. Therefore, gelation in the production of positive electrode paste and gas generation during the charging and discharging of lithium secondary batteries can be reduced.

[0030] ​Within the framework of this invention, at% represents atomic percentage. The at% or "atomic percentage" of a given element refers to the percentage of atoms of that element relative to all atoms in the claimed composition.

[0031] ICP-OES provides the weight percentage (wt%) of each element contained in a material by measuring its composition. The conversion from wt% to at% is as follows: the first element in the material... E 1 （E at1 ） The at% can be obtained from the first element in the material by applying the following formula. E 1 （E wt1 ） The given wt% conversion,

[0032] in E aw1 It is the first element E The standard atomic weight (molecular weight) of 1. E wti It is the first i element E i wt% E awi The first one is the one mentioned i element E i The standard atomic weight (molecular weight), and n It is an integer representing the number of all types of elements contained in the material.

[0033] In a preferred embodiment, M' comprises: - Ni with a content of x relative to M', where 0 at% ≤ x ≤ 30.0 at%. - Mn with a content of y relative to M', where 50.0 at% ≤ y ≤ 100.0 at%. -Co with a content of z relative to M', where 0.0 at% ≤ z ≤ 12.0 at%. - Ti with a content of a relative to M', where 0.0 at% -Al content b relative to M', where 0.0 at% ≤ b ≤ 2.0 at%. - Zr with a content of c relative to M', where 0.0 at% ≤ c ≤ 2.0 at%. ​- D with a content of d relative to M', wherein 0.0 at% ≤ d ≤ 2.0 at%, and D is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, La, Mg, Mo, Nb, S, Sr, V, W, Y and Zn; -Where x, y, z, a, b, c, and d are measured by ICP-OES; and -where x+y+z+a+b+c+d is 100.0 at.

[0034] In a preferred embodiment, the first lithium metal oxide contains at most 0.7% by weight, preferably at most 0.6% by weight, and more preferably at most 0.5% by weight of LiOH relative to the total weight of the first lithium metal oxide, wherein the content of LiOH is measured by acid-base titration as described in this specification.

[0035] In a preferred embodiment, the first lithium metal oxide contains at most 0.3% by weight, preferably at most 0.25% by weight, and more preferably at most 0.2% by weight of Li2CO3 relative to the total weight of the first lithium metal oxide, wherein the content of Li2CO3 is measured by acid-base titration as described in this specification.

[0036] In a preferred embodiment, 0.0 at%

[0037] In a preferred embodiment, 0.01 at% ≤ b ≤ 5.0 at% and 0.01 at% ≤ c ≤ 5.0 at%.

[0038] Method for manufacturing positive electrode active material powder In a second aspect, the present invention relates to a method for manufacturing a positive electrode active material powder according to the first aspect, wherein the method comprises the following sequential steps: -Step 1) A second lithium metal oxide containing Li, M'' and O is mixed with an aqueous solution to obtain a slurry, filtered, and then the slurry is dried to obtain a dry powder, wherein M'' is the same as M' except for Ti. -Step 2) Mix the dried powder with a Ti-containing compound, preferably TiO2, wherein the compound contains Ti in an amount between 300 ppm and 4000 ppm by weight relative to the dried powder, and - Step 3) Heat the mixture in an oxidizing atmosphere at a temperature between 450°C and 650°C to obtain the positive electrode active material powder.

[0039] ​The second lithium metal oxide can be prepared by lithiation of a (hydroxy) hydroxide containing M''. The surface area of ​​the second lithium metal oxide can be reduced in step 1), and the surface area of ​​the positive electrode active material powder can be further reduced in steps 2) and 3). Ti enrichment at grain boundaries is achieved through steps 2) and 3). The temperature in step 3) can be 450°C or higher, preferably 500°C or higher, more preferably 550°C or higher, and can be 650°C or lower, preferably 630°C or lower, more preferably 600°C or lower. If the temperature in step 3) is below 450°C or above 650°C, and / or if the amount of Ti added in step 2) is less than 300 ppm or more than 4000 ppm, Ti may not be sufficiently enriched at the grain boundaries. The surface area of ​​the positive electrode active material powder may decrease as the temperature in step 3) increases. Without being bound by any theory, if the temperature in step 3) is above 650°C, the decrease in surface area of ​​the positive electrode active material may not lead to improved electrochemical performance due to insufficient Ti enrichment at the grain boundaries.

[0040] In a preferred embodiment, the amount of Ti is between 500 ppm and 3000 ppm.

[0041] In a preferred embodiment, the temperature in step 3) is between 500 and 600°C.

[0042] In a preferred embodiment, the second lithium metal oxide further comprises Al and Zr.

[0043] In a preferred embodiment, the aqueous solution is deionized water.

[0044] Battery In a third aspect, the present invention relates to a battery comprising a positive electrode active material powder according to the first aspect.

[0045] Use of a battery pack In a fourth aspect, the present invention relates to the use of the battery according to the third aspect.

[0046] As will be understood by those skilled in the art, all embodiments relating to the positive electrode active material according to the first aspect are applicable in parallel to the second, third and fourth aspects.

[0047] Experimental tests used in the examples The following analysis methods were used in the example: A) Particle size distribution (PSD) analysis After dispersing the positive electrode active material powder as described below in an aqueous medium, the PSD was measured using a Malvern Mastersizer 3000 with a Hydro MV wet dispersion attachment. To improve the dispersion of the positive electrode active material powder examples, adequate ultrasonic irradiation and stirring were applied, and a suitable surfactant was introduced. D50 was defined as the particle size at 50% of the cumulative volume percentage distribution.

[0048] B) Inductively Coupled Plasma-Optical Emission Analysis (ICP-OES) Examples of positive electrode active materials described below were measured using inductively coupled plasma optical emission spectrometry (ICP-OES) with an Agilent ICP 720-OES instrument. One gram of powder sample from each example was dissolved in 50 mL of high-purity hydrochloric acid in an Erlenmeyer flask. The flask was covered with a watch glass and heated on a hot plate at 380°C until the sample was completely dissolved. After cooling to room temperature, the solution and rinsing water from the Erlenmeyer flask were transferred to a 250 mL volumetric flask. The volumetric flask was then filled to the 250 mL mark with DI water and thoroughly homogenized. A second dilution was performed by pipetting an appropriate amount of solution and transferring it to a 250 mL volumetric flask, which was then filled to the 250 mL mark with an internal standard and 10% hydrochloric acid and homogenized. Finally, this solution was used for ICP-OES measurements. The contents of Ni, Mn, Co, and Ti are expressed as at% of the total of these components.

[0049] C) Button battery testing C1. Button cell manufacturing To prepare the positive electrode, a slurry containing positive electrode active material powder, conductor (Super P, Timcal), and binder (KF#9305, Kureha) in a solvent (NMP, Mitsubishi) with a weight ratio of 96.5:1.5:2.0 was prepared using a high-speed homogenizer. The homogenized slurry was spread onto one side of an aluminum foil using a doctor blade coater with a 170 µm gap. The slurry-coated foil was dried in an oven at 120°C and then pressed using a calender. It was then dried again in a vacuum oven to completely remove any remaining solvent from the electrode film. The button cell was assembled in an argon-filled glove box. A separator (Celgard 2320) was positioned between the positive electrode and a piece of lithium foil used as the negative electrode. A 1M solution of LiPF6 in EC / DMC (1:2) was used as the electrolyte and dropped between the separator and the electrode. The button cell was then completely sealed to prevent electrolyte leakage.

[0050] C2. Test Method The test method is the standard "constant cutoff voltage" test. The standard button cell battery test in this invention follows the protocol shown in Table 1. Each battery is cycled at 25°C using a Toscat-3100 computer-controlled constant current cycling station (from Toyo).

[0051] This scheme uses a 1C current definition of 220 mA / g over a metal window ranging from 4.3 V to 3.0 V / Li. The capacity decay rate (QF) is obtained according to the following formula.

[0052]

[0053] Where DQ1 is the discharge capacity at the first cycle, DQ7 is the discharge capacity at the seventh cycle, and DQ34 is the discharge capacity at the thirty-fourth cycle.

[0054] The irreversible capacity (Qirr) (%) is obtained from the following equation:

[0055] CQ1 represents the charging capacity during the first cycle.

[0056] Table 1. Cyclic Scheme for Button Battery Testing

[0057] D) Surface alkalinity analysis The determination of soluble base content by pH titration involves two steps: (a) solution preparation and (b) pH titration. Detailed explanations of each step are as follows: Step (a): Solution preparation: Immerse the powder in deionized water and stir for 10 minutes in a sealed glass flask containing 100 ml of deionized water. The amount of positive electrode active material powder is 4 g. After stirring, to dissolve the alkali, filter the suspension of powder in water to obtain a clear solution.

[0058] Step (b): pH titration: The 90 ml clear solution prepared in step (a) was used for pH titration using 0.1 M HCl. The flow rate was 0.5 ml / min, and the pH value was recorded every 3 seconds. The pH titration curve (pH value as a function of added HCl) showed two distinct equivalence (or inflection point) points. The first equivalence point (corresponding to the amount of HCl in EP1) at approximately pH 7.4 was determined by OH-. - and CO3 2- With H + The reaction produces [the product]. At the second equivalence point around pH 4.7 (corresponding to the amount of HCl in EP2), [it is produced by] HCO3-. - With H +The reaction produces [the product]. It is speculated that the alkali dissolved in the deionized water is LiOH (in a quantity of 2 [units]). EP1-EP2) or Li2CO3 (amount of 2) (EP2-EP1)). The values ​​obtained for LiOH and Li2CO3 are the result of the surface reaction with deionized water.

[0059] E) Specific surface area analysis The specific surface area of ​​the positive electrode active material was measured using the Bruanauer-Emmett-Teller (BET) method with a Micromeritics Tristar II 3020 instrument. Prior to measurement, the powder sample was heated at 300ºC for 1 hour under nitrogen (N2) to remove adsorbed substances. The dried powder was then placed in a sample tube. The sample was then degassed at 30°C for 10 minutes. Nitrogen adsorption was tested at 77 K. The total specific surface area (in m²) of the sample was obtained by obtaining nitrogen isotherm adsorption / desorption curves. 2 / g).

[0060] F) Carbon analysis The carbon content of the positive electrode active material powder was measured using a Horiba Emia-Expert carbon / sulfur analyzer. One gram of the positive electrode active material powder was placed in a ceramic crucible within a high-frequency induction furnace. 1.5 grams of tungsten and 0.2 grams of tin were added to the crucible as promoters. The powder was heated at a programmable temperature, during which the gases produced in the combustion process were analyzed using an infrared detector. The carbon concentration was determined by analyzing CO2 and CO.

[0061] G) Scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) measurements To prepare thin sheets for cross-sectional scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS), positive electrode active material particles were coated with a 25 nm carbon layer (Leica EM ACE600 coating machine) prior to focused ion beam (FIB) preparation. FIB sheets were prepared on a Cu Omniprobe TEM grid using a Thermo Fisher Helios FIB-SEM with a Ga ion beam at 30 kV, then at 8 kV, and finally at 2 kV and 39 pA in a final thinning step. The sheet dimensions were approximately 4.2 × 6.6 μm, with a thickness of approximately 50–100 nm.

[0062] The thin section was transferred to an Ar-filled glove box within a vacuum transfer chamber. A TEM vacuum transfer holder (Gatan) was assembled within the glove box. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) were performed at 300 kV using a Super X detector on an aberration-corrected FEI Titan transmission electron microscope. The screen current was 150 pA, the acquisition time was 20 min, and the spectral size was 570 × 570 nm.

[0063] For EDX spectrum acquisition and data processing, Bruker's Esprit Quantax software version 1.9 was used. For line scan curves, the following elements were considered: Ni (Ni-K line at 7.47 keV), Mn (Mn-K line at 5.90 keV), Co (Co-K line at 6.93 keV), and Ti (Ti-K line at 4.51 keV).

[0064] The thickness of the grain boundary was determined by Ti concentration curves from line scans across the grain boundary. The amount of Ti was normalized by the total atomic fractions of Ni, Mn, Co, and Ti. The thickness of the grain boundary was measured as the width of the maximum Ti peak along the baseline of the line scan curve across the grain boundary.

[0065] Example The present invention is further illustrated in the following examples: Comparative Examples 1 to 4 Comparative Example 1 (CEX1) was prepared according to the following steps: 1) Coprecipitation: In a large continuous stirred tank reactor (CSTR), a metal with the composition Ni was prepared by coprecipitation using a mixture of nickel-manganese-cobalt-aluminum sulfate, sodium hydroxide, and ammonia. 0.91 Mn 0.04 Co 0.04 Al 0.01 Transition metal-based precursors.

[0066] 2) First mixing: 5000 g of the precursor prepared in step 1), 24.9 g of ZrO2, and 1354.6 g of LiOH as the lithium source were uniformly mixed to obtain a first mixture with a lithium to metal (Ni, Mn, Co, and Al) ratio of 1.06. The amount of ZrO2 was determined to be 3500 ppm relative to the weight of the precursor.

[0067] 3) First heating: The first mixture from step 2) is heated at 710°C for 12 hours in an oxygen atmosphere, then crushed and sieved to obtain the first heated product.

[0068] 4) Washing: The first heated product from step 3) is mixed with water at 5°C for 10 minutes to form a slurry. The ratio of the first heated product to water is 1:1. The slurry is filtered, vacuum dried at 140°C for 10 hours, and sieved to obtain a washed powder.

[0069] 5) Second mixing: Mix 500 g of the washed powder from step 4) with 0.88 g of TiO2 powder to obtain a second mixture containing 1000 ppm Ti by weight relative to the washed powder.

[0070] 6) Second heating: The second mixture from step 5) is heated at 300°C for 5 hours in an oxygen atmosphere, then pulverized and sieved to obtain CEX1 with a D50 of about 11.6 µm.

[0071] CEX2 is prepared using the same method as CEX1, except that the second heating temperature is 400°C.

[0072] CEX3 is prepared using the same method as CEX1, except that the first heated product in step 3) is not washed as in step 4) and is used directly in step 5) in place of the washed powder in step 4), and the second heating temperature is 600°C.

[0073] CEX4 is prepared using the same method as CEX1, except that the second heating temperature is 700°C.

[0074] Examples 1 to 3 EX1 is prepared using the same method as CEX1, except that the second heating temperature is 500°C.

[0075] EX2 is prepared using the same method as CEX1, except that the second heating temperature is 600°C.

[0076] EX3 was prepared using the same method as EX2, except that more TiO2 powder was added in the second mixing to obtain 2500 ppm Ti relative to the weight of the washed powder.

[0077] result Table 2 summarizes the methods and properties of the embodiments and comparative examples.

[0078] Table 2. Summary of methods and properties of the embodiments and comparative examples

[0079] The second heating temperature is the temperature applied in step 3) of the method according to the present invention.

[0080] Except for EX3, all examples and comparative examples consisted of positive electrode active material powders containing approximately 0.2 at% of Ti relative to the total content of Ni, Mn, Co, and Al in the positive electrode active material powder. The second heating temperature varied between 300°C and 700°C. EX1 to EX3, with second heating temperatures in the range of 500°C to 600°C, exhibited excellent electrochemical properties as tested by coin cell technology. This was indicated by higher DQ1, lower Qirr, and lower QF. EX3 contained approximately 0.44 at% of Ti in the positive electrode active material, and the second heating temperature was 600°C. A comparison of EX2 and EX3 showed that the second heating temperature had a greater effect on electrochemical properties than the amount of Ti, as EX2 and EX3 exhibited similar electrochemical properties even though the amount of Ti differed significantly.

[0081] The residual Li content on the surface of CEX3, prepared using the same method as EX2 (the difference being that CEX3 is not washed with aqueous solution), is significantly higher than that on the surface of EX2.

[0082] The electrochemical properties of CEX4 (prepared using the same method as EX2, except that the second heating temperature of CEX4 is 700°C), such as DQ1, Qirr, and QF, are not superior to those of EX2. Without being bound by any theory, the second heating temperature of 700°C may not lead to an improvement in electrochemical performance due to insufficient Ti enrichment at the grain boundaries, while the surface area of ​​CEX4 is reduced to 0.31 m². 2 / g.

[0083] Figure 1a , Figure 1b , Figure 1c , Figure 2a , Figure 2b and Figure 2c The study confirmed the enrichment of Ti in the grain boundaries. Figure 1a and Figure 2a These are cross-sectional STEM images of EX2 at different locations. In each image, the boundaries between adjacent primary particles are observed and marked with arrows. Figure 1b and Figure 2b They are the corresponding Figure 1a and Figure 2a EDS-mapped scan images. Figure 1b and Figure 2b The diagram shows Ti enrichment at grain boundaries. Specifically, the brighter area crossed by the arrow is a Ti-enriched region located at the boundary between adjacent primary grains.

[0084] Figure 1c and Figure 2c They are displayed separately. Figure 1b and Figure 2bThe arrows representing the respective Ti concentrations are EDS line scans of the regions traversed. The arrows also indicate the scan direction. Ti enrichment is clearly visible in each plot showing grain boundary thicknesses in the range of 20–50 nm. Figure 1c As shown, the maximum Ti concentration at grain boundaries is approximately 20% relative to the Ti concentration obtained by ICP-OES, compared to Ni, Mn, Co, and Ti. Figure 2c The results show that the maximum Ti concentration at grain boundaries, relative to Ni, Mn, Co, and Ti, is approximately 14 times the Ti concentration obtained by ICP-OES. This high proportion indicates that Ti is significantly enriched at grain boundaries, since Ti was added after washing EX2 with an aqueous solution.

Claims

1. A positive electrode active material powder suitable for use in a lithium-ion rechargeable battery, comprising secondary particles comprising a plurality of primary particles, wherein the positive electrode active material powder comprises a first lithium metal oxide comprising lithium, M’ and oxygen, wherein the first lithium metal oxide has a layered a-NaFe02 structure; wherein M’ comprises Ti and at least one element selected from the group consisting of nickel and manganese; wherein there are grain boundaries between adjacent primary particles of the secondary particles; wherein the concentration of Ti in the grain boundaries is greater than the concentration of Ti in the adjacent primary particles; wherein the positive electrode active material powder has a surface area, as determined by BET measurement, between 0.5 m 2 / g and 1.2 m 2 / g; and wherein the ratio of the maximum concentration of Ti in the grain boundaries to the Ti concentration obtained by ICP-OES is 5 or greater with respect to M’.

2. The positive electrode active material of claim 1, wherein the thickness of the grain boundaries is between 5 and 100 nm, preferably 10 and 80 nm and more preferably 20 and 50 nm.

3. The positive electrode active material powder of claim 1 or 2, wherein M’ comprises: - Ni in an amount x with respect to M’, wherein 70.0 at% < x < 100.0 at%, - Mn in an amount y with respect to M’, wherein 0.0 at% < y < 11.0 at%, - Co in an amount z with respect to M’, wherein 0.0 at% < z < 11.0 at%, - Ti in an amount a with respect to M’, wherein 0.0 at% < a < 2.0 at%, - Al in an amount b with respect to M’, wherein 0.0 at% < b < 2.0 at%, - Zr in an amount c with respect to M’, wherein 0.0 at% < c < 2.0 at%, - D in an amount d with respect to M’, wherein 0.0 at% < d < 2.0 at%, wherein D is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, La, Mg, Mo, Nb, S, Sr, V, W, Y and Zn; - wherein x, y, z, a, b, c and d are measured by ICP-OES; and - wherein x + y + z + a + b + c + d is 100.0 at%.

4. The positive electrode active material powder of claim 1 or 2, wherein M’ comprises: - Ni in an amount x with respect to M’, wherein 0 at% < x < 30. 0 at%, - Mn in an amount y with respect to M’, wherein 50.0 at% < y < 100.0 at%, - Co in an amount z with respect to M’, wherein 0.0 at% < z < 12.0 at%, - Ti in an amount a with respect to M’, wherein 0.0 at% < a < 2.0 at%, - Al in an amount b with respect to M’, wherein 0.0 at% < b < 2.0 at%, - Zr in an amount c with respect to M’, wherein 0.0 at% < c < 2.0 at%, - D in an amount d relative to M', wherein 0.0 at% < d < 2.0 at%, wherein D is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, La, Mg, Mo, Nb, S, Sr, V, W, Y and Zn; - wherein x, y, z, a, b, c and d are measured by ICP-OES; and - wherein x+y+z+a+b+c+d is 100.0 at%.

5. Positive electrode active material powder according to any one of the preceding claims, wherein the first lithium metal oxide comprises LiOH in an amount of at most 0.7 wt% relative to the total weight of the first lithium metal oxide, and wherein the amount of LiOH is measured by acid-base titration.

6. Positive electrode active material powder according to any one of the preceding claims, wherein the first lithium metal oxide comprises Li2CO3 in an amount of at most 0.3 wt% relative to the total weight of the first lithium metal oxide, and wherein the amount of Li2CO3 is measured by acid-base titration.

7. Positive electrode active material powder according to any one of the preceding claims, wherein 0.0 at% < a < 1.0 at%.

8. Positive electrode active material powder according to any one of the preceding claims, wherein 0.01 at% < b < 5.0 at% and 0.01 at% < c < 5.0 at%.

9. Positive electrode active material powder according to any of the preceding claims, wherein the surface area is between 0.6 m 2 / g and 1.1 m 2 / g.

10. A method for manufacturing a positive electrode active material powder according to any one of the preceding claims, wherein the method comprises the following consecutive steps: - Step 1) mixing a second lithium metal oxide comprising lithium, M" and oxygen, with an aqueous solution to obtain a slurry, filtering, and then drying the slurry to obtain a dry powder, wherein M" is the same as M' except for Ti, - Step 2) mixing the dry powder with a compound comprising Ti, preferably TiO2, wherein the compound comprises Ti in an amount of between 300 ppm and 4000 ppm relative to the weight of the dry powder, and - Step 3) heating the mixture in an oxidizing atmosphere at a temperature between 450 °C and 650 °C to obtain the positive electrode active material powder.

11. Method according to claim 10, wherein the amount of Ti is between 500 ppm and 3000 ppm.

12. Method according to claim 11 or 12, wherein the temperature in step 3) is between 500 and 600 °C.

13. Method according to any one of claims 10 to 12, wherein the second lithium metal oxide further comprises Al and Zr.

14. A battery comprising the positive electrode active material powder according to any one of claims 1 to 9.

15. Use of the battery according to claim 14 in an electric vehicle or in a hybrid electric vehicle.

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