Cathode active material and lithium-ion secondary battery

Abstract

The present invention relates to a cathode active material powder suitable for lithium-ion rechargeable batteries, comprising lithium, M', and oxygen, wherein M' comprises: Ni in a content x, wherein 0.0 ≤ x ≤ 50.0 mol%, relative to M', Mn in a content y, wherein 50.0 ≤ y ≤ 90.0 mol%, relative to M', Co in a content z, wherein 0.0 ≤ z ≤ 40.0 mol%, relative to M', at least one element selected from the group consisting of Al, B, Ba, Ce, Fe, La, Mg, Mo, Nb, S, Sr, Ti, V, Cr, Ca, Zr, Hf, Ta, Y, Zn and W, in a content d, 0.0≤d≤ 10.0 mol%, relative to M'; wherein x, y, z, and d are measured by ICP-OES; and wherein x+y+z+d is 100.0 mol%; and wherein the cathode active material has a specific surface area of at least 0.4 m2 / g as determined by BET measurement, and a FWHM(104)c / FWHM(003)c ratio of at most 4.0 as determined by X-Ray diffraction analysis using Cu-Kα ray, wherein FWHM(104)c is a full width at half maximum of the peak in a range of 2θ = 43°-45° after instrument correction and FWHM(003)c is a full width at half maximum of a peak in a range of 2θ = 17°-20° after instrument correction.

Description

[0001] CATHODE ACTIVE MATERIAL AND LITHIUM-ION SECONDARY BATTERY

[0002] TECHNICAL FIELD

[0003] The present invention relates to cathode active materials for secondary batteries. Particularly, however not exclusively, the present invention concerns cathode active material powder suitable for lithium-ion rechargeable batteries and batteries manufactured thereof.

[0004] BACKGROUND

[0005] Lithium-ion secondary batteries typically include a negative electrode (anode), an electrolyte, and a positive electrode (cathode) that contains a lithium-transition metal oxide as an active material capable of lithium insertion and desorption. Lithium-transition metal oxides are generally manufactured from transition-metal hydroxides, oxides or oxyhydroxide, generally referred as precursors. These precursors are typically produced through coprecipitation processes involving the mixing of a metal salt solution and an alkali solution in the presence of a complexing agent. Commonly used metals are transition metals such as nickel, manganese, and cobalt. A manufacturing process for cathode active materials typically includes mixing a precursor material with a source of lithium, sintering, and, when necessary, also milling. Examples of such cathode active materials include lithium nickel manganese cobalt oxides, abbreviated as NMC, Li-NMC, LNMC, or NCM.

[0006] As cathode active materials play a critical role in rechargeable batteries and exert a significant impact on the overall battery performance, there has been extensive research and development in this field in recent years, encompassing their precursors. Several trends in the development of cathode active materials include, among others, enhancing capacity retention, achieving higher energy densities, improving stability and cycling performance, and reducing costs. Modifying the transition metal stoichiometry changes the material's properties, providing a way to adjust cathode performance. However, in the case of a NMC-based battery, increasing the nickel content enhances its initial discharge capacity but diminishes its thermal stability and capacity retention. Elevating cobalt content involves replacing either higher- energy nickel or chemically stable manganese, in addition to being cost-prohibitive. Conversely, increasing manganese content results in reduced capacity performance for the manufactured battery due to its lower nickel content.

[0007] There is thus a need for improved cathode active materials to address the above- mentioned problems.

[0008] SUMMARY OF THE INVENTION

[0009] The present invention aims at providing manganese-rich cathode active material having an advantageous microstructure particularly suitable to be applied in high power battery applications, including electric vehicles. By providing the manganese-rich cathode active material having a unique combination of specific surface area and FWHM(io4)c / FWHM(oo3)c ratio, the discharge capacity demands can be met.

[0010] In a first aspect, the invention can provide a cathode active material powder suitable for lithium-ion rechargeable batteries, comprising lithium, M', and oxygen, wherein M' comprises

[0011] - Ni in a content x, wherein 0.0 < x < 50.0 mol%, relative to M',

[0012] - Mn in a content y, wherein 50.0 < y < 90.0 mol%, relative to M',

[0013] - Co in a content z, wherein 0.0 < z < 40.0 mol%, relative to M',

[0014] - at least one element selected from the group consisting of Al, B, Ba, Ce, Fe, La, Mg, Mo, Nb, S, Sr, Ti, V, Cr, Ca, Zr, Hf, Ta, Y, Zn and W, in a content d, 0.0<d<10.0 mol%, relative to M';

[0015] - wherein x, y, z, and d are measured by ICP-OES; and

[0016] - wherein x+y+z+d is 100.0 mol%; and wherein the cathode active material has a specific surface area of at least 0.4 m2 / g as determined by BET measurement and a FWHM(io4)c / FWHM(oo3)c ratio of at most 4.0 as determined by X-Ray diffraction analysis using Cu-Ko ray, wherein FWHM(io4)c is a full width at half maximum of the peak in a range of 29 = 43°-45° after instrument correction and FWHM(OO3)C is a full width at half maximum of a peak in a range of 29 = 17°-20° after instrument correction. The term "instrument correction" is readily understood by the skilled person in the art performing X-Ray diffraction analysis. Said instrument correction refers to correcting instrument broadening with a standard NIST (National Institute of Standards and Technology) sample, for example LaB6standard. The specific surface area typically expressed in unit m2 / g, may be measured according to a well standardized methodology ISO 9277.

[0017] The combined characteristics according to the invention, i.e. the disclosed ranges of the transition metal stoichiometry, the specific surface area, and the FWHM(io4)c / FWHM(oo3)c ratio, surprisingly contributes to uncompromised battery electrochemical properties such as discharge capacity and efficiency value, even though having a relatively low amount of nickel.

[0018] Thus, in a second aspect, the invention can provide a lithium-ion secondary battery comprising a cathode which comprises a cathode active material according to the first aspect of the invention.

[0019] In addition, in a third aspect, the invention provides a method of manufacturing a cathode active material, comprising the steps of: mixing a precursor material for the cathode active material, a lithium source, and optionally a dopant source, to obtain a mixture; wherein the precursor material has a tap density, TD, of at least 1.65 g / cm3and a ratio of a specific surface area, SSA, to the tap density, SSA / TD, of at least 12.00, expressed in unit (m2* cm3) / g2; heating the mixture in oxidizing atmosphere at a temperature between 650°C to 1000°C, preferably between 700°C to 950°C, more preferably between 800°C to 950°C, to obtain the cathode active material. The main embodiments are characterized in the independent claims. Various embodiments are disclosed in the dependent claims. The embodiments and examples recited in the claims and the specification are mutually freely combinable unless otherwise explicitly stated.

[0020] DETAILED DESCRIPTION OF THE INVENTION

[0021] In the following detailed description, preferred embodiments are described in detail to enable practice of the invention. Although the invention is described with reference to these specific preferred embodiments, it will be understood that the invention is not limited to these preferred embodiments. To the contrary, the invention includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description and accompanying drawings. In this specification, if any numerical ranges are provided, the ranges include also the upper and lower values unless otherwise explicitly stated.

[0022] The term "comprising", as used herein and in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a composition comprising components A and B" should not be limited to compositions consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the composition are A and B. Accordingly, the terms "comprising" and "including" encompass the more restrictive terms "consisting essentially of" and "consisting of".

[0023] In a first aspect, the invention can provide a cathode active material powder suitable for lithium-ion rechargeable batteries, comprising lithium, M', and oxygen, wherein M' comprises

[0024] - Ni in a content x, wherein 0.0 < x < 50.0 mol%, relative to M',

[0025] - Mn in a content y, wherein 50.0 < y < 90.0 mol%, relative to M',

[0026] - Co in a content z, wherein 0.0 < z < 40.0 mol%, relative to M',

[0027] - at least one element selected from the group consisting of Al, B, Ba, Ce, Fe, La, Mg, Mo, Nb, S, Sr, Ti, V, Cr, Ca, Zr, Hf, Ta, Y, Zn and W, in a content d, 0.0<d< 10.0 mol%, relative to M';

[0028] - wherein x, y, z, and d are measured by ICP-OES; and

[0029] - wherein x+y+z+d is 100.0 mol%; and wherein the cathode active material has a specific surface area of at least 0.4 m2 / g as determined by BET measurement and a FWHM(io4)c / FWHM(oo3)c ratio of at most 4.0 as determined by X-Ray diffraction analysis, wherein FWHM(i04)c is a full width at half maximum of the peak in a range of 29 = 43°-45° after instrument correction and FWHM(003)c is a full width at half maximum of a peak in a range of 20 = 17°-20° after instrument correction. The term "instrument correction" is readily understood by the skilled person in the art in X-Ray diffraction analysis. Said instrument correction refers to correcting instrument broadening with a standard NIST (National Institute of Standards and Technology) sample, for example LaB6standard.

[0030] The values x, y, z, d can be measured by Inductively Coupled Plasma Optical Emission spectroscopy (ICP-OES) method. It can be understood that the expression >0 in the chemical formulas includes the absence of an element.

[0031] In X-Ray Diffraction (XRD) analysis, X-ray diffraction profiles are broadened depending on the instrumental and optical conditions used, the instrumental broadening being related to the breadth of the X-ray source, flat specimen surface and axial divergence of the X-ray beam. The usual way to take care of the instrumental broadening in peak profile analysis is to measure a well-defined standard sample as for example the NIST SMR660a LaB6standard. This standard material is characterized by a perfect crystal structure, a well-known grain size distribution, and diffraction peaks well distributed along the Bragg angle. Methods of instrument correction is well known in the art. For example, correction for instrument broadening may be done by subtracting the corresponding extrapolated FWHM of the LaB6standard. An example of X-Ray Diffraction (XRD) analysis including instrument correction is illustrated under EXAMPLE item C) in the present disclosure. In other words, a FWHM after instrument correction, such as FWHM(i04)c or FWHM(003)c, may be obtained by:

[0032] - obtaining X-ray diffractograms of a LaB6standard material and a cathode active material,

[0033] - performing K- a2 correction by applying the Rachinger correction, to obtain a K- a2 corrected pattern,

[0034] - performing background correction from the K-a2 corrected XRD pattern, to obtain a background corrected pattern,

[0035] - obtaining FWHM of (003) peak and (104) peak and FWHM of LaB6from the K-a2 and background corrected XRD pattern,

[0036] - obtaining an instrument corrected FWHM (i.e. FWHM(i04)c and FWHM(003)c) from the FWHM of (003) peak and (104) peak and FWHM of LaB6by subtracting the corresponding extrapolated FWHM of the LaB6. For example: The instrument corrected FWHM of the (003) peak may be obtained by:

[0037] FWHM^ = FWHM(OO3) - FWHMa°

[0038] In this formula FWHM(oos) is the FWHM of the (003) peak obtained from the background and K-a2 corrected XRD pattern. FWHM^ is the FWHM of LaB6obtained from the background and K-a2 corrected XRD pattern.

[0039] Preferably, the positive electrode active material powder comprises particles having a layered structure belonging to a space group R-3m. The particles may have an additional structure belonging to a space group C2 / m. The crystal structure of the layered structure can be identified from a powder X-ray diffraction pattern obtained from powder X-ray diffractometry using CuKo as a radiation source.

[0040] The specific surface area, typically expressed in unit m2 / g, may be measured according to a well standardized methodology ISO 9277. As appreciated by the skilled person, the specific surface area can be measured, for example, with the Brunauer-Emmett-Teller (BET) method by using, for example, a Quantachrome Monosorb.

[0041] The combined characteristics according to the invention, i.e. the disclosed ranges of the transition metal stoichiometry, the specific surface area, and the FWHM(io4)c / FWHM(oo3)c ratio, surprisingly contributes to uncompromised battery electrochemical properties such as discharge capacity and efficiency value, even though having a relatively low amount of nickel, as it had been believed in the state of the art that reducing nickel content in the cathode active material adversely impacts the discharge capacity of batteries made therefrom.

[0042] The cathode active material powder according to the first aspect of the invention has the Ni content x of at most 50 mol%, preferably at most 45 mol%, and preferably at least 10 mol%, more preferably at least 15 mol%, and most preferably at least 25 mol%. In some embodiments, 15.0 < x < 45.0 mol%. The disclosed lower limits are beneficial for a satisfactory capacity.

[0043] The cathode active material powder according to the first aspect of the invention has the manganese content y of at least 50 mol%, preferably at least 55 mol%, and more preferably at least 60 mol%. In some embodiments, content y is at most 80 mol% or at most 70 mol%. In some embodiments, 55.0 < y < 80.0 mol%.

[0044] The cathode active material powder according to the first aspect of the invention has a cobalt content z of at most 40 mol%, preferably at most 20 mol%.

[0045] In some embodiments, the cathode active material according to the invention wherein M' comprises

[0046] 10.0 < x < 50.0 mol%, relative to M',

[0047] 50.0 < y < 90.0 mol%, relative to M',

[0048] 0.0 < z < 20.0 mol%, relative to M',

[0049] 0.0 < d < 2.0 mol%, relative to M'.

[0050] According to the invention, it is advantageous that the cathode active material has a high specific surface area of at least 0.4 m2 / g, preferably at least 0.45 m2 / g, more preferably at least 0.5 m2 / g, and most preferably at least 0.6 m2 / g, as determined by BET measurement. Having a disclosed lower limit of the specific surface area may enhance ion diffusion, and this allows for faster charging and discharging, leading to higher power density and improved performance. On the other hand, an excessively high surface area might affect the full-cell cycle life and might cause gassing issues. In some embodiments, the specific surface area is at most 5.00 m2 / g, preferably at most 4.50 m2 / g, more preferably at most 4.00 m2 / g. According to the invention, it is advantageous that the cathode active material has a FWHM(io4)c / FWHM(oo3)c ratio of at most 4.0. It is found that a cathode active material having a specific surface area of at least 0.4 m2 / g and having a FWHM(io4)c / FWHM(oo3)c ratio excessing 4.0, affects adversely both the initial capacity efficiency and the discharge capacity of the battery provided with such cathode active material. Without intending to be bound by any theory, a cathode active material having an excessively large FWHM(io4)c / FWHM(oo3)c ratio, such as more than 4.0, may have insufficient crystal growth, and in a battery provided with such a cathode active material, there is a concern that the metal element in the cathode active material may be easily eluted in the electrolyte during high temperature storage or the like. Elution of such metal elements can cause the capacity deterioration of the battery. From the viewpoint of capacity retention at high temperature storage, the FWHM(io4)c / FWHM(oo3)c ratio of the cathode active material is suitably at most 3.8, preferably at most 3.5, more preferably at most 3.4.

[0051] The lower limit of the FWHM(io4)c / FWHM(oo3)c ratio is not particularly limited, but a FWHM(io4)c / FWHM(oo3)c ratio of 1.5 or more is preferable. In some embodiments, the FWHM(io4)c / FWHM(oo3)c ratio is at least 1.7, preferably at least 2.0.

[0052] In some embodiments, the cathode active material according to the invention has a median particle size, D50, of at least 5.00 pm, as determined by laser diffraction; preferably the D50 is at most 12.00 pm, more preferably at most 10.00 pm, for example at most 8.0 pm. In some embodiments, the cathode active material according to the invention has a span value, defined as (D90 - D10) I D50, of at most 1.00, preferably at most 0.70, more preferably at most 0.50, and most preferably at most 0.45. The span value may be at least 0.20, for example at least 0.30, or at least 0.35. As appreciated by the skilled person, the particle size distribution can be analyzed by using a Malvern Mastersizer 3000 with a Hydro MV wet dispersion unit after dispersing particles of a sample in an aqueous medium. It is found that the disclosed ranges of D50 and / or span value, in combination of the disclosed ranges of specific surface area, are advantageous in the electrochemical properties of the cathode active material, indicated by the discharge capacity of the batteries.

[0053] Sodium and sulfur are generally considered as impurities. A high level of impurities may affect performance of the cathode active material. It is preferable that the cathode active material has a sodium content of at most 100 ppm, preferably at most 80 ppm, more preferably at most 70 ppm. It is preferable the cathode active material has a sulfur content of at most 5000 ppm, for example at most 3000 ppm. However, it is also preferable that the sulfur content is at least 300 ppm, for example at least 450 ppm, or at least 1400 ppm.

[0054] The invention also provides a method of manufacturing a cathode active material, comprising the steps of: mixing a precursor material for the cathode active material, a lithium source, and optionally a dopant source, to obtain a mixture; wherein the precursor material has a tap density, TD, of at least 1.65 g / cm3and a ratio of a specific surface area, SSA, to the tap density, SSA / TD, of at least 12.00, expressed in unit (m2* cm3) / g2; heating the mixture in oxidizing atmosphere at a temperature between 650°C to 1000°C, preferably between 700°C to 950°C, more preferably between 800°C to 950°C, to obtain the cathode active material. The precursor comprise M and element oxygen, wherein M may comprise Ni in a content a, wherein 0.0 < a < 50.0 mol%, relative to M, Mn in a content b, wherein 50.0 < b < 90.0 mol%, relative to M, Co in a content c, wherein 0.0 < c < 40.0 mol%, relative to M, at least one dopant in a content t, 0.0<t< 10.0 mol%, relative to M; wherein a, b, c, and t are measured by ICP-OES; and wherein a+b+c+t is 100.0 mol%.

[0055] The tap density, typically expressed in unit g / cm3, may be measured according to a well standardized methodology ISO 3953, or equivalently ASTM B 527. The tap density of the precursor may be at least 1.70 g / cm3, or the tap density may be at most 2.00 g / cm3, for example at most 1.90 g / cm3, or at most 1.80 g / cm3.

[0056] The specific surface area of the precursor may be at least 25.00 m2 / g, for example at least 30.00 m2 / g, or at least 33.00 m2 / g.

[0057] The SSA / TD ratio may be at least 14.00, and / or at most 30.00, for example at most 25.00.

[0058] The precursor may have a total pore volume of at least 0.100 cm3 / g determined from nitrogen adsorption measurement and calculated according to the BJH; and the total pore volume may be for example at most 0.200 cm3 / g, or at most 0.180 cm3 / g.

[0059] EXAMPLES

[0060] The present invention is further illustrated with reference to some examples and comparative examples.

[0061] The following analysis methods are used in the examples:

[0062] A) Particle size distribution (PSD) analysis

[0063] The PSD is measured using a Malvern Mastersizer 3000 with Hydro MV wet dispersion accessory after dispersing examples as described below of cathode active material powders in an aqueous medium. To improve the dispersion of the cathode active material powder examples, sufficient ultrasonic irradiation and stirring is applied, and an appropriate surfactant is introduced. D50 is defined as the particle size at 50% of the cumulative volume % distribution.

[0064] B) Inductively coupled plasma - optical emission analysis (ICP-OES) analysis

[0065] The cathode active material examples as described herein below are measured by the Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) method using an Agillent ICP 720-OES. 1 gram of a powder sample of each example is dissolved into 50 mL high purity hydrochloric acid in an Erlenmeyer flask. The flask is covered by a watch glass and heated on a hot plate at 380°C until complete dissolution of the sample. After being cooled to room temperature, the solution and the rinsing water of Erlenmeyer flask are transferred to a 250 mL volumetric flask. Afterwards, the volumetric flask is filled with DI water up to the 250 mL mark, followed by complete homogenization. An appropriate amount of solution is taken out by pipette and transferred into a 250 mL volumetric flask for the 2nddilution, where the volumetric flask is filled with internal standard and 10% hydrochloric acid up to the 250 mL mark and then homogenized. Finally, this solution is used for ICP-OES measurement. The contents of elements such as Li, Ni, Mn, Co, Al, B, Ba, Ce, Fe, La, Mg, Mo, Nb, S, Sr, Ti, V, Cr, Ca, Zr, Hf, Ta, Y, Zn and W are expressed as at% or mol%..

[0066] C) X-Ray Diffraction (XRD) analysis

[0067] Cl) XRD measurement

[0068] The X-ray diffraction pattern of the cathode active material powder examples as described herein below is collected with a Bruker D8 Advance using a Cu Ko radiation source (40 kV, 40 mA) emitting at a wavelength of 1.5418 A. The instrument configuration is set at: a 2.5° primary soller slit, 0.5° divergent slit, and an automatic antiscatter slit. Detector opening is 3.296°.

[0069] The XRD pattern should satisfy the following requirements. Data points are collected with a small step width not exceeding 0.02°, preferably 0.01° or less. The peak to background ratio (based on the number of counts) near the (003) peak of cathode active material powder examples should be at least 25: 1, preferably 100: 1 or higher. The peak intensity should be at least 10,000 counts or higher to achieve low relative scattering. The XRD measurement is applied to the cathode active material powder examples as well as a standard material of XRD measurement, preferably LaB6which is used since it has a high crystallinity and relatively many peaks. The XRD measurement parameters like slit settings, scan time and etc. are applied in a way to achieve a high-quality pattern as described above. In addition, slit settings need to allow for a low instrument broadening. Instrument broadening is sufficiently low. For example, if the K-al component of the (Oil) peak of LaB6near 30.5° as well as the K-al component of the (001) peak of LaB6near 21.2° have FWHM values below 0.1°, preferably below 0.08°. If the FWHM values exceeds these values, the instrument correction to the experimentally obtained FWHM is unreliable.

[0070] Diffraction patterns are obtained separately for XRD standard material LaB6and the cathode active material with below conditions:

[0071] LaB6standard material is scanned in the range of 18 to 50° to obtain (001) peak at around 21.3°, (Oil) peak at around 30.5°, (111) peak at around 37.5°, (002) peak at around 43.5° and (021) peak at around 49°

[0072] Cathode active material is scanned in the range of 15 - 50° (29) with a scan time / step of 0.24 second and a step-size of 0.015° per scan to obtain (003) peak at around 18.5° and (104) peak at around 44.5°. C2) Diffractogram analysis

[0073] X-ray diffractograms of both LaB6standard material and the cathode active material obtained from Cl) are analyzed according to the steps 1-4 below to obtain a corrected FWHM data for cathode active material:

[0074] 1) K- oc2 correction by applying the Rachinger correction,

[0075] 2) Background correction,

[0076] 3) Obtain FWHM,

[0077] 4) Correct for instrument broadening (by subtracting the corresponding extrapolated FWHM of the LaB6 standard).

[0078] Step 1) K- 2 correction (Rachinger correction)

[0079] Input: measured XRD pattern;

[0080] Output: K-a2 corrected XRD pattern

[0081] Generally, a measured XRD pattern is a superposition of two patterns: A first pattern caused by the Cu Koi radiation and second pattern due to the Cu Ko2 radiation. Therefore, unless Ko2 component can be filtered by the XRD machine, a correction is required to obtain FWHM data. The Koi and Ko2 patterns are basically identical, but the Ko2 pattern is at a slightly higher scattering angle and has about Vi of the intensity.

[0082] By using the wavelength 1.540 A for Cu Koi and 1.544 A for Cu Ko2 and assuming that the intensity of the Ko2 pattern is 50% of the Koi pattern, Ko2 pattern can be eliminated from the measured pattern and thereby obtain a calculated Koi pattern. In other words, the measured pattern is corrected for the Ko2 pattern and the calculated Koi pattern well represents the real Koi pattern.

[0083] This correction is the so-called Rachinger correction.

[0084] The Rachinger correction (or similar approaches to correct for Ko2) are part of commercial XRD packages and any suitable program can be used to do the Ko2 correction. However, if such a package is not existed, it is possible to do the correction for example by an excel file and a few lines of code.

[0085] The Rachinger correction uses the following formula as the relation between scattering angle for Koi and Ko2:

[0086] 180

[0087] 20,f(zl= 2 -

[0088] Ko2 correction is applied by a recursive formula:

[0089] In this formula IKai(x) is the corrected intensity at the scattering angle x In practice the correction starts from the 1st(smallest) 20 =20(Ko2) point and loops towards larger angles.

[0090] Since the measured pattern is present at discrete points, intensities IKai(20(Kal) are obtained by interpolation from the neighbor points and a few initial points will be missing or be corrected incorrectly. However after very few iterations the correction is stable.

[0091] Step 2) Background correction

[0092] Input: K-a2 corrected XRD pattern;

[0093] Output: K-a2 and background corrected pattern

[0094] Background correction can be performed by any suitable state of art XRD software or following the procedure below:

[0095] For the cathode active material, the 20 position xmax of the peak maximum of the (003) and (104) peak is obtained, respectively. A region for averaging of intensities is defined according to Table 1 below. The center of mass in these regions defines the corresponding average background points.

[0096] For example, for the (003) peak the intensities for all points within the region ranging from 3° left of xmax to 2° left of xmax are averaged. The resulting left background point is (x,y) = (xmax -2.5, mean intensity). Similarly, the intensities of all points within the region ranging from 0.7° right of xmax to 1.7° right of xmax are averaged. The resulting right background point is (x,y) = (xmax +1.2, mean intensity). The straight line connecting the left and right background point is the background line. The background and K-a2 corrected (003) peak pattern is obtained by subtracting the background line between the left and right background point from the K-a2 corrected intensities.

[0097] The procedure for (104) is similar using the values for the (104) peak in Table 1.

[0098] Table la. Definition of regions for (003) and (104) of the cathode active material for the calculation of the linear background. xmax is the 20 value of the point of max. intensity of the corresponding peak.

[0099] Table lb. Definition of regions for (001) and (002) of LaB6for the calculation of the linear background. xmax is the 20 value of the point of max. intensity of the corresponding peak.

[0100] Step 3) Obtain FWHM

[0101] Input: K-a2 and background corrected pattern;

[0102] Output: FWHM of (003) and (104) and FWHM of LaB6

[0103] The FWHM of the (003) and (104) peak is obtained from the K-a2 and background corrected XRD pattern. The FWHM is the distance in degree of 29 from the left crossing of the horizontal Vi max line with the XRD pattern to the right crossing of the Vi max line with the XRD pattern. The left crossing point refers to the cross of the Vi max line with the line connecting the last XRD point below and the first XRD point above the Vi max line.

[0104] The right crossing point refers to the cross of the Vi max line with the line connecting the last point after the maximum above the Vi max line and the 1stpoint after the maximum below the Vi max line. Hereby Vi max refers to a horizontal line where the intensity value is1 / 2 of the intensity of the maximum point of the corresponding peak of the background and K-a2 corrected pattern.

[0105] Similarly, the FWHM of the LaB6standard is obtained: The FWHM is obtained by the same procedure above (Rachinger correction, background correction, obtain FWHM). In the case of a LaB6standard the XRD measurement should cover the 29 range of 18-50° Within this region LaB6has 5 strong peaks: (001), (Oil), (111), (002) and (021) at approx, positions 21.3, 30.5, 37.5, 43.5 and 49°.

[0106] Step 4) Instrument correction

[0107] Input: FWHM of (003) and (104) and FWHM of LaB6;

[0108] Output: instrument corrected FWHM of (003) and (104)

[0109] The (003) peak of a cathode active material (~ 18.5°) is adjacent to the (001) peak of LaB6. The (104) peak of a cathode active material is adjacent to the (002) peak of LaB6. Thus, the FWHM of the LaB6(001) is used to instrument correct the cathode active material (003) peak, and the FWHM of the LaB6(002) is used to instrument correct the cathode active material (104) peak, respectively.

[0110] The instrument correction is applied by subtraction the FWHM of LaB6from the FWHM of the cathode active material. For example: The instrument corrected FWHM of the (003) peak is obtained by:

[0111] In this formula FWHM(oos) is the FWHM of the (003) peak obtained from the background and K-a2 corrected XRD pattern. FWHM^ is the FWHM of LaB6obtained from the background and K-a2 corrected XRD pattern.

[0112] In the same way, the instrument corrected FWHM of the (104) peak is obtained by:

[0113] In this formula FWHM(i04) is the FWHM of the (104) peak obtained from the background and K-a2 corrected XRD pattern. FWHM^ is the FWHM of LaB6obtained from the background and K-a2 corrected XRD pattern.

[0114] D) Coin cell testing DI) Coin cell preparation

[0115] For the preparation of a positive electrode (cathode), a slurry that contains a cathode active material powder, conductor (Li-435, Denka) comprising dispersing agent (NBR), and binder (KF#9700, Kureha) - with a formulation of 92.2:3.3:4.5 by weight - in a solvent (NMP, Mitsubishi) is prepared by a high-speed homogenizer. The homogenized slurry is spread on one side of an aluminum foil using a doctor blade coater with a 180 pm gap. The slurry coated foil is dried in an oven at 120°C and then pressed using a calendaring tool. Then it is dried again in a vacuum oven to completely remove the remaining solvent in the electrode film. A coin cell is assembled in an argon-filled glovebox. A separator (Celgard 2320) is located between a positive electrode (cathode) and a piece of lithium foil used as a negative electrode. Mixture of LiPF6in EC / EMC + LiBF4+ FEC is used as electrolyte and is dropped between separator and electrodes. Then, the coin cell is completely sealed to prevent leakage of the electrolyte.

[0116] D2) Testing method

[0117] The testing method in the present invention follows the schedule shown in Table 2. Each cell is cycled using a Toscat-3100 computer-controlled galvanostatic cycling station (from Toyo).

[0118] The schedule uses a 1C current definition of 200 mAh / g in two steps:

[0119] Cycle 1 at 4.65 V to 2.0 V / Li metal window range.

[0120] Cycle 2 and cycle 3 at 4.40 V to 2.5 V / Li metal window range

[0121] DQ3 is a discharge capacity of the third cycle.

[0122] Table 2. Cycling schedule for Coin cell testing method

[0123] Example 1

[0124] (1) Precursor A preparation step

[0125] (la) Seed slurry preparation process

[0126] First, a starting solution was prepared by placing 10 L of DI water, 0.1 L of 55 g / L aqueous solution of ammonia and 0.1 L of 220 g / L NaOH solution in a 30 L reaction vessel equipped with a turbine-type impeller located 50 mm from the bottom of the vessel. The reactor temperature was adjusted to 45 °C and kept at this temperature throughout the process. An inert atmosphere was inside the reaction vessel was ensured by feeding N2gas with the flow rate of 0.3 m3 / h.

[0127] Next, 130 g / L metal sulfate solution comprising Ni and Mn (in a stoichiometric molar ratio, Ni : Mn of 35 : 65), 55 g / L aqueous solution of ammonia and 220 g / L NaOH solution were continuously added with feed rates of 1.7 L / h, of 0.046 L / h, and of 1.44 L / h, respectively. The reaction mixture was stirred with the stirring speed of 1200 rpm. A NH3(aq) concentration in the reaction mixture was kept between 1.2-1.5 g / L and pH of the reaction mixture was kept between 12.1-12.25 by adjusting the feeding of the aqueous solution of ammonia and the feeding of NaOH solution, respectively. The reaction was done in a continuous mode. When the reaction reached a stable state, a reaction resultant, i.e. the aqueous slurry of particles Nio.3sMno.65(OH)2having D50 of 1.3 pm, was collected from the overflow of the reaction vessel.

[0128] (lb) Particle growth process

[0129] First, a starting solution was prepared by placing 3.6 L of DI water in an 8.75 L reaction vessel equipped with two A45-type impellers, of which lower one was located 65 mm from the bottom of the vessel and the upper one located 140 mm up from the lower impeller. After starting to feed the gases of N2and O2inside the reaction vessel in such a way that the O2content in the reaction vessel atmosphere was maintained at 0.75 vol. % an amount of 400 mL of the prepared seed slurry of particles Nio.3sMno.65(OH)2having D50 of 1.3 pm (a seed amount was 48 g) was mixed with DI water. The pH of the starting solution was adjusted with 220 g / L NaOH(aq) to the value of 9.6 (measured at a temperature of 20 °C) and the reaction vessel was heated to 45 °C, Next, a crystallization of the particles of the starting solution was continued by a precipitation reaction performed by adding 120 g / L metal sulfate solution comprising Ni and Mn (in a stoichiometric molar ratio, Ni : Mn of 35 : 65) at a constant rate of 960 mL / h and 220 g / L NaOH(aq) solution in such a way that the pH value of the reaction mixture in the reaction vessel was raised from the pH value of the starting solution and kept between the maximum of 10.8 and the minimum of 10.7 (measured at a temperature of 20 °C). The reaction mixture was stirred with the stirring speed of 1200 rpm for the first 2 hours, followed with 800 rpm for the next 2 hours, with 600 rpm for the next 14 hours and then with 500 rpm, respectively, for the rest of the precipitation process. During the growth process a part of a liquid fraction (i.e. mother liquid) of the reaction mixture was pumped out from the reaction vessel by using a concentrator (i.e. a mother liquid filtration device) to maintain and increase solid phase content in the reaction vessel. The reaction was terminated after 50 hours from the start.

[0130] The obtained slurry was filtered and washed with 220 g / L NaOH(aqj solution and 60 °C DI water, followed by a heat treatment in an air atmosphere with 120 °C for 12 hours drying to obtain a oxyhydroxide powder presented by a general formula: Nio.35Mn0.65-Oa(OH)2-a, wherein 0 < a < 2, a cathode active material precursor A.

[0131] The precursor A powder and a lithium hydroxide powder were weighted in such a way that the ratio Li / Me between the number of moles of Li (mol) of lithium and the total number of moles of Me (mol) of the transition metals (Ni and Mn) was 1.35 and mixed. Then the mixture was heated in a furnace to Tmax=850 °C in a flow of oxygen gas of 20 L / min and continuing the sintering for 8 hours. After cooling, the sample was sieved to obtain a powder of a cathode active material labelled as EX1.1.

[0132] Further three cathode active materials were similarly prepared except Tmax was 875 °C, 905 °C, and 925 °C, and labelled as EX1.2, EX1.3, and EX1.4, respectively.

[0133] Example 2

[0134] A precursor B was prepared according to the same procedures as precursor A, except that in the particle growth process the gases of N2and O2were fed inside the reaction vessel in such a way that O2content in the reaction vessel atmosphere was maintained at 1.55 vol. %, the starting solution pH was 11.1 which was then kept between the maximum of 11.0 and the minimum of 10.9 during the precipitation reaction, the reaction mixture was stirred with the stirring speed of 1200 rpm for the first 2 hours, followed of 800 rpm for the next 2 hours and then of 600 rpm, respectively, for the rest of the precipitation process, and the reaction was terminated after 38 hours. Cathode active material EX2.1 - EX2.4 cathode active materials EX2.1-EX2.4 are prepared according to the same method as EX1.1-EX1.4 except that precursor B was used instead of precursor A. Temperature for each sample are listed in the Table 3.

[0135] Example 3

[0136] A precursor C was prepared according to the same procedures as precursor A, except that in the particle growth process the starting solution pH was 10.0 which was then raised and kept between the maximum of 10.9 and the minimum of 10.7 during the precipitation reaction.

[0137] Cathode active material EX3.1 and EX3.2

[0138] Cathode active materials EX3.1 and EX3.2 are prepared according to the same method as EX1.1 and EX1.4 except that precursor C was used instead of precursor A. Temperature for each sample are listed in the Table 3.

[0139] Example 4

[0140] A precursor D was prepared according to the same procedures as precursor A, except that in the seed slurry preparation process the used metal sulfate solution comprised only nickel sulfate (i.e. NiSC ) and the NH3(aq) concentration in the reaction mixture was kept between 2.1 - 3.7 g / L and pH of the reaction mixture was kept between 12.4-12.7 by adjusting the feeding of the aqueous solution of ammonia and the feeding of NaOH solution, respectively, that in the particle growth process an amount of 350 mL of the prepared seed slurry of particles Ni(OH)2having D50 of 1.5 pm (a seed amount was 46 g) was admixed, the starting solution pH was 10.6 which was then raised and kept between the maximum of 10.9 and the minimum of 10.7 during the precipitation reaction and the reaction was terminated after 24 hours from the start.

[0141] Cathode active material EX4.1 and EX4.2

[0142] Cathode active materials EX4.1 and EX4.2 are prepared according to the same method as EX1.1 and EX1.4 except that precursor D was used instead of precursor A. Temperature for each sample are listed in the Table 3.

[0143] Example 5

[0144] A precursor E was prepared according to the same procedures as precursor A, except in the particle growth process the starting solution pH was 9.8 which was then raised and kept between the maximum of 11.0 and the minimum of 10.7 during the precipitation reaction.

[0145] Cathode active material EX5 was prepared according to the same method as EX1.4 except that precursor E was used instead of precursor A. Temperature for each sample are listed in the Table 3.

[0146] Comparative Example 1

[0147] A precursor F was prepared according to the same procedures as precursor A, except in the particle growth process 2.7 L of DI water and 800 mL of the prepared seed slurry of particles Nio.3sMno.65(OH)2having D50 of 1.5 pm (a seed amount was 96 g) was added in the reaction vessel equipped with a turbine impeller which located 65 mm from the bottom, the gas of N2gas was fed inside the reaction vessel without any O2gas to maintain an inert reaction vessel atmosphere, the feed rate of the metal sulfate solution was 1200 mL / h, the starting solution pH was 11.0 which was then kept between the maximum of 11.1 and the minimum of 10.6 during the precipitation reaction, and the reaction mixture was stirred with the stirring speed of 1000 rpm for the first 2 hours, followed of 800 rpm for the rest of the precipitation process. The reaction was terminated after 46 hours. cathode active materials CEX1.1-CEX1.4 are prepared according to the same method as EX1.1-EX1.4 except that precursor F was used instead of precursor A. Temperature for each sample are listed in the Table 3.

[0148] Comparative Example 2

[0149] A precursor G was prepared according to the same procedures as precursor A, except in the particle growth process 3.25 L of DI water and 250 mL of the prepared seed slurry of particles Nio.3sMno.65(OH)2having D50 of 1.3 pm (a seed amount was 30 g) was added in the reaction vessel equipped with a turbine impeller which located 46 mm from the bottom. N2gas was fed inside the reaction vessel without any O2gas to maintain an inert reaction vessel atmosphere, the starting solution pH was 10.4 which was then kept between the maximum of 11.1 and the minimum of 10.9 during the precipitation reaction, the reaction mixture was stirred with the stirring speed of 850 rpm for the first 2 hours, followed of 700 rpm for the next 2 hours and then of 600 rpm, respectively, for the rest of the precipitation process, and the reaction was terminated after 22 hours. (2) Cathode active material CEX2.1-CEX2.4 preparation step cathode active materials CEX2.1-CEX2.4 are prepared according to the same method as EX1.1-EX1.4 except that precursor G was used instead of precursor A. Temperature for each sample are listed in the Table 3.

[0150] Comparative Example 3

[0151] (1) Precursor H preparation step

[0152] A precursor H was prepared according to the same procedures as precursor A, except in the particle growth process a 200 L reaction vessel equipped with turbine-type impeller located 80 mm from the bottom of the vessel was used, the starting solution was prepared by adding 100 L water and 15 L of the prepared seed slurry of particles Ni (OH)2having D50 of 1.5 pm of example 4 (a seed amount was 1.8 kg) and adjusting the pH to a value of 10.4, during the precipitation reaction the metal sulfate solution was fed at a constant rate of 25 L / h, the pH value of the reaction mixture in the reaction vessel was raised from the pH value of the starting solution and kept between the maximum of 10.9 and the minimum of 10.7 (measured at a temperature of 20 °C), the gases of N2and O2were fed inside the reaction vessel in such a way that O2content in the reaction vessel atmosphere was maintained at 4.2 vol. %, the reaction mixture was stirred with the stirring speed of 550 rpm for the first 2 hours, followed of 400 rpm for the next 2 hours, followed of 300 rpm for the next 18 hours and then of 200 rpm, respectively, for the rest of the precipitation process, and the reaction was terminated after 38 hours.

[0153] (2) Cathode active material CEX3.1 and CEX3.2 preparation step cathode active materials CEX3.1 and CEX3.2 are prepared according to the same method as EX1.1 and EX1.4 except that precursor H was used instead of precursor A. Temperature for each sample are listed in the Table 3.

[0154] Results

[0155] Table 3. Properties of example and comparative example. Table 3 summarizes the properties of examples and comparative example. Examples are the cathode active material with surface area of at least 0.4 m2 / g and FWHM(i04)c / FWH M(OO3)C ratio of at most 4.0. Such cathode active material exhibit improved electrochemical properties indicated by high DQ3.

Claims

CLAIMS1. A cathode active material powder suitable for lithium-ion rechargeable batteries, comprising lithium, M', and oxygen, wherein M' comprises:- Ni in a content x, wherein 0.0 < x < 50.0 mol%, relative to M',- Mn in a content y, wherein 50.0 < y < 90.0 mol%, relative to M',- Co in a content z, wherein 0.0 < z < 40.0 mol%, relative to M',- at least one element selected from the group consisting of Al, B, Ba, Ce, Fe, La, Mg, Mo, Nb, S, Sr, Ti, V, Cr, Ca, Zr, Hf, Ta, Y, Zn and W, in a content d, 0.0<d< 10.0 mol%, relative to M';- wherein x, y, z, and d are measured by ICP-OES; and- wherein x+y+z+d is 100.0 mol%; and wherein the cathode active material has a specific surface area of at least 0.4 m2 / g as determined by BET measurement, and- a FWHM(io4)c / FWHM(oo3)c ratio of at least 1.7 and at most 4.0 as determined by X-Ray diffraction analysis using Cu-Ko ray, wherein FWHM(io4)c is a full width at half maximum of the peak in a range of 20 = 43°-45° after instrument correction and FWHM(003)c is a full width at half maximum of a peak in a range of 20 = 17°-20° after instrument correction.

2. The cathode active material according to claim 1, wherein:10.0 < x < 50.0 mol%, relative to M',50.0 < y < 90.0 mol%, relative to M',0.0 < z < 20.0 mol%, relative to M',0.0 < d < 2.0 mol%, relative to M'.

3. The cathode active material according to any of previous claims, wherein the specific surface area is at least 0.45 m2 / g.

4. The cathode active material according to any of previous claims, wherein the specific surface area is at most 5.00 m2 / g, preferably at most 4.50 m2 / g, more preferably at most 4.00 m2 / g.

5. The cathode active material according to any of previous claims, wherein the specific surface area is at least 0.50 m2 / g, preferably at least 0.60 m2 / g.

6. The cathode active material according to any of previous claims, wherein the FWHM(io4)c / FWHM(oo3)c ratio is at most 3.8, preferably at most 3.5, more preferably at most 3.4.

7. The cathode active material according to any of previous claims, wherein the FWHM(io4)c / FWHM(oo3)c ratio is preferably at least 2.0.

8. The cathode active material according to any of previous claims, wherein 15.0 < x < 45.0 mol%.

9. The cathode active material according to any of previous claims, wherein 55.0 < y < 80.0 mol%.

10. A battery comprising the cathode active material powder according to any one of claims 1 to 9.

11. Use of the battery according to claim 10 in an electric vehicle or in a hybrid electric vehicle.

12. A method of manufacturing the cathode active material according to any of claims 1 to 9, comprising the steps of: mixing a precursor material for the cathode active material, a lithium source, and optionally a dopant source, to obtain a mixture; wherein the precursor material has a tap density, TD, of at least 1.65 g / cm3and a ratio of a specific surface area, SSA, to the tap density, SSA / TD, of at least 12.00, expressed in unit (m2* cm3) / g2; heating the mixture in oxidizing atmosphere at a temperature between 650°C to 1000°C, preferably between 700°C to 950°C, more preferably between 800°C to 950°C, to obtain the cathode active material.

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