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

Abstract

The present invention is related to a positive electrode active material powder for lithium-ion rechargeable batteries, wherein the positive electrode active material powder comprises particles, wherein each of the particles consists of at least one primary particle and at most twenty primary particles, wherein the positive electrode active material powder essentially comprises Li, Ni, Mn, Al, and O, and wherein Al is introduced by (i) adding a material formed by heating a mixture comprising a Li source and a transition metal composite precursor essentially comprising Ni and Mn to an aqueous solution comprising a Al-containing compound and (ii) milling the material. Due to the aforementioned introduction of Al, the positive electrode active material powder may have a ratio of Ni3+ to Ni2+ as measured by XPS being at least 1.45.

Description

[0001] Positive electrode active material powder and method for manufacturing a positive electrode active material powder

[0002] TECHNICAL FIELD

[0003] The present invention relates to a positive electrode active material powder for lithium-ion rechargeable batteries. In detail, the present invention relates to a positive electrode active material powder comprising particles, wherein each of the particles consists of at least one primary particle and at most twenty primary particles, and comprises lithium, oxygen, nickel, manganese and aluminum; a method for preparing said positive electrode active material powder; and a battery comprising said positive electrode active material powder.

[0004] BACKGROUND

[0005] The demand for lithium-ion rechargeable batteries has been consistently high in recent years due to their widespread use in various applications such as consumer electronics, electric vehicles (EVs), energy storage systems, and more. In order to develop lithium-ion rechargeable batteries with longer cycle life and lower direct current resistance ("DCR"), much research has been conducted on positive electrode active material powders that could achieve such high performance.

[0006] Adding aluminum (Al) to a positive electrode active material powder comprising lithium (Li), nickel (Ni) and manganese (Mn) has been tried to improve the performance of batteries. KR2019 / 0079526A ("KR'526") discloses a polycrystalline positive electrode active material powder, which was prepared by mixing a core comprising Li, Ni, Mn and cobalt (Co) with sources of Al, tungsten (W) and boron (B), and then heating the mixture to form a surface layer on the core in order to suppress the increase of DCR and improve capacity retention. WO2022 / 129077A1 ("WO'077") discloses a single crystalline positive electrode active material powder prepared by dry mixing a core comprising Li, Ni, Mn and Co with powders containing W, Al and B and then heating the mixture to form a surface layer on the core.

[0007] However, since a polycrystalline positive electrode active material powder tends to suffer from severe side reactions along grain boundaries during cycling in a battery, the positive electrode active material powder of KR'526 is not sufficient to achieve desirable long cycle life and low DCR of batteries. In addition, since the surface layer on the core of the positive electrode active material powder of WO'077 is not highly homogeneous, there is still room for improving the cycle life and DCR growth of the battery comprising the positive electrode active material powder of WO'077. It is a first object of the present invention to provide a positive electrode active material powder comprising Al to improve the performance of the battery comprising the positive electrode active material powder, in particular longer cycle life and lower DCR growth.

[0008] It is a second object of the present invention to provide a method for preparing said positive electrode active material powder.

[0009] It is a third object of the present invention to provide a battery comprising said positive electrode active material powder.

[0010] SUMMARY OF THE INVENTION

[0011] The first object is achieved by providing a positive electrode active material powder for lithium-ion rechargeable batteries, wherein the positive electrode active material powder comprises particles, wherein each of the particles consists of at least one primary particle and at most twenty primary particles, wherein the positive electrode active material powder comprises Li, M', and O, wherein M' comprises:

[0012] - Ni in a content x, wherein 45.0 at% < x < 95.0 at%, relative to M',

[0013] - Mn in a content y, wherein 0.0 at% < y < 30.0 at%, relative to M',

[0014] - Co in a content z, wherein 0.0 at% < z < 20.0 at%, relative to M',

[0015] - D in a content a, wherein 0.0 at% < a < 2.0 at%, relative to M', wherein D comprises at least one element selected from Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, Zn, and Zr, and

[0016] - Al in a content b, wherein 0.00 at% < b < 1.00 at%, relative to M',

[0017] - B in a content c, wherein 0.00 at% < c < 1.00 at%, relative to M', and

[0018] - W in a content d, wherein 0.00 at% < d < 1.00 at%, relative to M', wherein x, y, z, a, b, c, and d are measured by ICP-OES, wherein x+y+z+a + b+c+d is 100.0 at%, and wherein a ratio of Ni3+to Ni2+of the positive electrode active material powder as measured by X-ray Photoelectron Spectroscopy (XPS) is at least 1.45, preferably at least 1.50, more preferably at least 1.60, most preferably at least 1.65.

[0019] The present inventors have surprisingly found that the positive electrode active material powder of the present invention improves the electrochemical performance of batteries, as demonstrated in the appended examples. Specifically, the positive electrode active material powder of the present invention prolongs the cycle life and lowers the DCR growth and the capacity fading of batteries.

[0020] Without wishing to be bound by any theory, the present inventors have found that introduction of Al by the method comprising (i) forming a first mixture comprising a Li source and a transition metal composite precursor, wherein the transition metal composite precursor comprises Ni, Mn, and, optionally, Co; (ii) heating the first mixture at a temperature between 650 °C and 1100 °C for 5 to 20 hours to obtain a heated material; and (iii) adding the heated material to an aqueous solution comprising a Al-containing compound, and milling the heated material to obtain a milled material may result in a homogeneous surface layer containing Al on the core of the positive electrode active material powder. The increase of the ratio of Ni3+to Ni2+of the present invention may be attributed to the homogeneous surface layer of Al. Furthermore, the increase of the ratio of Ni3+to Ni2+results in the improved electrochemical performance of the batteries comprising the present invention.

[0021] The second object is achieved by providing a method comprising (i) forming a first mixture comprising a Li source and a transition metal composite precursor, wherein the transition metal composite precursor comprises Ni, Mn, and, optionally, Co; (ii) heating the first mixture at a temperature between 650 °C and 1100 °C for 5 to 20 hours to obtain a heated material; and (iii) adding the heated material to an aqueous solution comprising a Al-containing compound, and milling the heated material to obtain a milled material.

[0022] The third object is achieved by providing a battery comprising said positive electrode active material powder according to the present invention.

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024] In the following detailed description, preferred embodiments are described in detail to enable practice of the present invention. Although the present 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 present invention includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description and accompanying drawings.

[0025] "about" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1% or less of and from the specified value, in so far such variations are appropriate to perform in the disclosed invention. However, it is to be 25 understood that the value to which the modifier "about" refers is itself also specifically disclosed.

[0026] "at%" signifies atomic percentage. The at% or "atomic percent" of a given element means a percentage of atoms of said element among all atoms in a claimed composition. ICP-OES provides weight percent (wt%) of each element included in a material whose composition is determined by this technique. Conversion from wt% to at% is as follows: at% of a first element Ei Eati) in a material can be converted from a given wt% of said first element Ei Ev / ti) in said material by applying the following formula, wherein Eawi is a standard atomic weight (molecular weight) of the first element Ei, Ewti is wt% of an ithelement Ei, Eawi is a standard atomic weight (molecular weight) of said ithelement Ei, and n is an integer which represents the number of types of all elements included in the material.

[0027] Positive Electrode Active Material Powder

[0028] In a first aspect, the present invention relates to a positive electrode active material powder for lithium-ion rechargeable batteries, wherein the positive electrode active material powder comprises particles, wherein each of the particles consists of at least one primary particle and at most twenty primary particles, wherein the positive electrode active material powder comprises Li, M', and O, wherein

[0029] M' comprises:

[0030] - Ni in a content x, wherein 45.0 at% < x < 95.0 at%, relative to M',

[0031] - Mn in a content y, wherein 0.0 at% < y < 30.0 at%, relative to M',

[0032] - Co in a content z, wherein 0.0 at% < z < 20.0 at%, relative to M',

[0033] - D in a content a, wherein 0.0 at% < a < 2.0 at%, relative to M', wherein D comprises at least one element selected from Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, Zn, and Zr, and

[0034] - Al in a content b, wherein 0.00 at% < b < 1.00 at%, relative to M',

[0035] - B in a content c, wherein 0.00 at% < c < 1.00 at%, relative to M', and

[0036] - W in a content d, wherein 0.00 at% < d < 1.00 at%, relative to M', wherein x, y, z, a, b, c, and d are measured by ICP-OES, wherein x+y+z+a + b+c+d is 100.0 at%, and wherein a ratio of Ni3+to Ni2+of the positive electrode active material powder as measured by XPS is at least 1.45, preferably at least 1.50, more preferably at least 1.60, most preferably at least 1.65.

[0037] In the frame work of the present invention, the particles, wherein each of the particles consists of at least one primary particle and at most twenty primary particles, are referred to as monolithic particles. At least 30% of the particles, more preferably at least 50% of the particles, constituting the powder observed in a SEM image is the monolithic particles. The number of primary particles constituting the monolithic particle is determined in a field of view of at least 45 pm x at least 60 pm ( / .e. of at least 2700 pm2), preferably of: at least 100 pm x 100 pm ( / .e. of at least 10,000 pm2). The particles in the image should be well distributed therefore avoiding overlap between particles. This can be achieved by pouring a small amount of powder sample to the adhesive attached on the SEM sample holder and blowing air to remove the excess powder. In the context of the present invention primary particles are distinguished from each other in a SEM image by observing grain boundaries between the primary particles. A grain boundary is defined as the interface between two primary particles, preferably wherein the atomic planes of the two primary particles are aligned to different orientations and meet as a crystalline discontinuity.

[0038] The monolithic particles can maintain their morphological integrity in the absence of anisotropic forces even if operated under extreme conditions, and thus, microcracks responsible for the degradation of the positive electrode active material powder, e.g., the decreased cycle life and the increased impedance, can be reduced.

[0039] In the frame work of the present invention, ICP-OES is Inductively Coupled Plasma Optical Emission Spectrometry, and the measurement method by ICP-OES is described in "EXPERIMENTAL ANALYSIS USED IN THE EXAMPLES, A) Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) measurement." In addition, XPS is X-ray Photoelectron Spectroscopy, and the measurement method by XPS is described in "EXPERIMENTAL ANALYSIS USED IN THE EXAMPLES, B) X-ray Photoelectron Spectroscopy."

[0040] The present inventors have found that a homogeneous surface layer containing Al on a core may result in the increase of the ratio of Ni3+to Ni2+. The homogeneous surface layer may be formed bythe method comprising (i) forming a first mixture comprising a Li source and a transition metal composite precursor, wherein the transition metal composite precursor comprises Ni, Mn, and, optionally, Co; (ii) heating the first mixture at a temperature between 650 °C and 1100 °C for 5 to 20 hours to obtain a heated material; and (iii) adding the heated material to an aqueous solution comprising a Al-containing compound, and milling the heated material to obtain a milled material. The positive electrode active material powder comprising the particles having said homogeneous surface layer may have the ratio of Ni3+to Ni2+of at least 1.45, preferably at least 1.50, more preferably at least 1.60, much more preferably at least 1.65, most preferably at least 1.70, and at most 2.50, preferably at most 2.20, more preferably at most 2.00, much more preferably at most 1.90, most preferably at most 1.80. The increased ratio of Ni3+to Ni2+results in the increase of the cycle life, the decrease of DCR growth, and the decrease of capacity fading. Without wishing to be bound by any theory, the homogeneous surface layer containing Al may suppress generation of Ni2+, which causes cation mixing, / .e., migration of Ni2+to vacant sites of Li+. The cation mixing may introduce structural instabilities, causing phase transitions or structural degradation during chargedischarge cycles. This instability can lead to capacity fading, reduced cycle life, and overall degradation of the positive electrode active material powder. The ratio of Ni3+to Ni2+may increase as the content of Ni, / .e., x, is increased. In a preferred embodiment, AIXPS / AIICP > 101.0, preferably AIXPS / AIICP > 105.0, more preferably AIXPS / AIICP > 107.0, most preferably AIXPS / AIICP > 109.0, and AIXPS / AIICP < 200.0, preferably AIXPS / AIICP < 170.0, more preferably AIXPS / AIICP < 160.0, most preferably AIXPS / AIICP < 150.0, AIXPS being a content of Al in at% relative to M', as measured by XPS analysis, and AIICP being a content of Al in at% relative to M', as measured by ICP-OES.

[0041] In a preferred embodiment, BXPS / BICP > 100.0, preferably BXPS / BICP > 110.0, more preferably BXPS / BICP > 120.0, most preferably BXPS / BICP > 130.0, and BXPS / BICP < 200.0, preferably BXPS / BICP < 170.0, more preferably BXPS / BICP < 160.0, most preferably BXPS / BICP < 150.0, BXPS being a content of B in at% relative to M', as measured by XPS analysis, and BICP being a content of B in at% relative to M', as measured by ICP-OES.

[0042] In a certain embodiment BXPS / BICP > 120.0, preferably BXPS / BICP > 125.0, more preferably BXPS / BICP > 130.0.

[0043] In a preferred embodiment, WXPS / WICP > 10.0, preferably WXPS / WICP > 13.0, more preferably WXPS / WICP > 15.0, most preferably WXPS / WICP > 17.0, and WXPS / WICP < 50.0, preferably WXPS / WICP < 40.0, more preferably WXPS / WICP < 35.0, most preferably WXPS / WICP < 28.0, WXPS being a content of W in at% relative to M', as measured by XPS analysis, and WICP being a content of W in at% relative to M', as measured by ICP-OES.

[0044] In a preferred embodiment, 70.0 at% < x < 80.0 at%, preferably 72.0 at% < x < 78.0 at%, more preferably 73.0 at% < x < 76.0, most preferably x is about 75.0 at%.

[0045] In a preferred embodiment, 20.0 at% < y < 30.0 at%, preferably 22.5 at% < y < 27.5 at%, more preferably 24.0 at% < y < 26.0 at%, most preferably y is about 25.0 at%.

[0046] In a preferred embodiment, 0.0 at% < z < 5.0 at%, preferably 0.0 at% < z < 3.0 at%, more preferably 0.0 at% < z < 1.0 at%, most preferably z is about 0.0 at%.

[0047] In a preferred embodiment, 0.0 at% < a < 1.5 at%, preferably 0.0 at% < a < 1.3 at%, more preferably 0.0 at% < a < 1.0 at%, most preferably a is about 0.0 at%.

[0048] In a preferred embodiment, 0.02 at% < b < 0.95 at%, preferably 0.03 at% < b < 0.93 at%, more preferably 0.04 at% < b < 0.92 at%, most preferably 0.10 at% < b < 0.80 at%.

[0049] In a preferred embodiment, 0.02 at% < c < 0.95 at%, preferably 0.03 at% < c < 0.93 at%, more preferably 0.04 at% < c < 0.92 at%, most preferably 0.10 at% < c < 0.80 at%. In a preferred embodiment, 0.02 at% < d < 0.95 at%, preferably 0.03 at% < d < 0.80 at%, more preferably 0.04 at% < d < 0.70 at%, most preferably 0.08 at% < d < 0.50 at%.

[0050] The positive electrode active material powder comprising the particles having the surface layer containing Al may result in more increased cycle life, more decreased DCR growth and more decreased capacity fading by further adding W and / or B to the surface layer.

[0051] In a preferred embodiment, the positive electrode active material powder according to the first aspect of the present invention is represented by formula (I):

[0052] LiwN ixiM nyiCoziDaiAlbiBci WdiO? (I) wherein 0.90 < w < 1.10, preferably 0.92 < w < 1.08, more preferably 0.95 < w < 1.05; wherein 0.45 < xl < 0.95, preferably 0.70 < xl < 0.80, more preferably 0.72 < xl < 0.78; wherein 0.00 < yl < 0.30, preferably 0.20 < yl < 0.30, more preferably 0.23 < yl < 0.28; wherein 0.00 < zl < 0.20, preferably 0.00 < zl < 0.05, more preferably 0.00 < zl < 0.03, most preferably zl is about 0.0; wherein 0.000 < al < 0.020, preferably 0.000 < al < 0.015, more preferably 0.000 < al < 0.013, most preferably al is about 0.0; wherein 0.0000 < bl < 0.0100, preferably 0.0002 < bl < 0.0095, more preferably 0.0003 < bl < 0.0093; wherein 0.0000 < cl < 0.0100, preferably 0.0002 < cl < 0.0095, more preferably 0.0003 < cl < 0.0093; wherein 0.0000 < dl < 0.0100, preferably 0.0002 < dl < 0.0095, more preferably 0.0003 < dl < 0.0093; and wherein xl+yl+zl+al + bl+cl+dl = 1.0.

[0053] Method for Preparing Positive Electrode Active Material Powder

[0054] In a second aspect, the present invention is related to a method for preparing the positive electrode active material powder according to the first aspect, comprising:

[0055] Step 1) forming a first mixture comprising a Li source and a transition metal composite precursor, wherein the transition metal composite precursor comprises Ni, Mn, and, optionally, Co;

[0056] Step 2) heating the first mixture at a temperature between 650 °C and 1100 °C, preferably between 750 °C and 1050 °C, more preferably between 800 °C and 1000 °C, most preferably between 850 °C and 950 °C for 5 to 20 hours, preferably for 6 to 18 hours, more preferably for 7 to 15 hours, most preferably for 8 to 12 hours to obtain a heated material; Step 3) adding the heated material to an aqueous solution comprising a Al-containing compound, and milling the heated material to obtain a milled material;

[0057] Step 4) drying the milled material to obtain a dried material;

[0058] Step 5) mixing the dried material, a B-containing compound, and a W-containing compound to obtain a second mixture; and

[0059] Step 6) heating the second mixture at a temperature between 250 °C and 500 °C preferably between 270 °C and 450 °C, more preferably between 300 °C and 425 °C, most preferably between 325 °C and 400 °C for 5.0 to 20.0 hours, preferably for 5.5 to 15.0 hours, more preferably for 6.0 to 12.0 hours, most preferably for 7.0 to 10.0 hours to obtain the positive electrode active material powder.

[0060] In a preferred embodiment, the Li source is LiOH. Li2COs as a Li source usually requires a high temperature to complete the synthesis of a positive electrode active material powder. This high temperature can damage the crystal structure of the positive electrode active material powder and change the oxidation state of Ni, leading to a poor performance of the battery. On the contrary, LiOH allows rapid and complete synthesis at lower temperature, resulting in a longer battery life cycle and enhanced safety features.

[0061] In a preferred embodiment, the transition metal composite precursor is (oxy)hydroxide or oxide comprising MP', wherein Mp' comprises:

[0062] - Ni in a content x2, wherein 45.0 at% < x2 < 95.0 at%, preferably 70.0 at% < x2 < 80.0 at%, relative to MP',

[0063] - Mn in a content y2, wherein 0.0 at% < y2 < 30.0 at%, preferably 20.0 at% < y2 < 30.0 at%, relative to Mp',

[0064] - Co in a content z2, wherein 0.0 at% < z2 < 20.0 at%, preferably 0.0 at% < z2 < 5.0 at% relative to Mp', and

[0065] - D2 in a content a2, wherein 0.0 at% < a2 < 2.0 at%, preferably 0.0 at% < a2 < 1.3 at%, relative to Mp', wherein D2 comprises at least one element selected from Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, Zn, and Zr.

[0066] In a preferred embodiment, the Al-containing compound is at least one selected from the group consisting of aluminum sulfate (Ah(SO4)3), aluminum oxide (AI2O3), aluminum hydroxide (AI(OH)s) and aluminum nitrate (AI(NO3)s). The Al-containing compound is preferably Al2(SO4)s.

[0067] In a preferred embodiment, the B-containing compound is at least one selected from the group consisting of orthoboric acid (H3BO3), boron carbide (B4C), boron trioxide (B2O3), isopropyl borate ((CsHyO^B), triphenyl borate ((CeHsC sB), tributyl borate ([CH3(CH2)3O]3B), phenylboronic acid (C6HsB(OH)2), and diboron tetrafluoride (B2F4). The B-containing compound is preferably H3BO3.

[0068] In a preferred embodiment, the W-containing compound is at least one selected from the group consisting of tungsten trioxide (WO3), tungsten carbide (WC), and tungsten nitride (WN). The W-containing compound is preferably WO3.

[0069] In a preferred embodiment, the milling in Step 3) is wet ball milling. Milling is the action of reducing the size of particles by a mechanical action submitting the particles to a stress. Some cracks will appear under the stress, and subsequently the particle will be broken in different parts. Wet ball milling is for milling solids in wet phase by introducing a liquid. It is basically a ball milling, wherein a rotating vessel filled with a grinding media as well as a product is rotated such that the grinding media should impact and / or apply a shear stress to the product. The apparatus of wet ball milling may be equipped with an agitator, which moves to make the grinding media impact or friction the particles to be milled.

[0070] In a preferred embodiment, the heated material in Step 3) is mixed with an aqueous solution. The aqueous solution may be deionized water. The grinding media may be at least one selected from the group consisting of zirconium oxide (ZrCh), alumina (AI2O3) and WC beads. The grinding media may have a diameter between 0.5 mm and 20.0 mm, preferably 5.0 mm and 15.0 mm, more preferably between 8.0 mm to 12.0 mm.

[0071] In a preferred embodiment, the drying in Step 4) is conducted at 100 to 200 °C, preferably at 110 to 190 °C, more preferably at 120 to 180 °C, most preferably at 130 to 170 °C.

[0072] In a preferred embodiment, the method according to the second aspect of the present invention further comprises mixing the positive electrode active material powder with alumina to form a third mixture, grinding the third mixture to form a grinded material, and sieving the grinded material. The grinding and sieving may be conducted by using air classifying mill (ACM).

[0073] Battery

[0074] In a third aspect, the present invention relates to a battery comprising the positive electrode active material powder according to the first aspect.

[0075] Use of Battery

[0076] In a fourth aspect, the present invention relates to a use of the battery according to the third aspect. As appreciated by a person skilled in the art, all embodiments directed to the positive electrode active material powder according to the first aspect may apply mutatis mutandis to the second, third and fourth aspects.

[0077] EXPERIMENTAL ANALYSIS USED IN THE EXAMPLES

[0078] The following analysis methods are used in the Examples.

[0079] A) Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) measurement

[0080] The amount of Li, Ni, Co, Mn, Al, B, W and D in the positive electrode active material powder is measured with the inductively coupled plasma - optical emission spectrometry (ICP-OES) method by using an Agilent ICP 720-ES (Agilent Technologies). 2 grams of powder sample is dissolved into 10 mL of high purity hydrochloric acid (at least 37 wt% of HCI with respect to the total weight of solution) in an Erlenmeyer flask. The flask is covered by a glass and heated on a hot plate at 380 °C until complete dissolution of the precursor. After being cooled to room temperature, the solution of the Erlenmeyer flask is poured into a 250 mL volumetric flask. Afterwards, the volumetric flask is filled with deionized water up to the 250 mL mark, followed by complete homogenization.

[0081] B) X-ray Photoelectron Spectroscopy (XPS)

[0082] In the present invention, X-ray photoelectron spectroscopy (XPS) is used to analyze the surface of positive electrode active material powder particles. In XPS measurement, the signal is acquired from the first few nanometers (e.g., 1 nm to 10 nm) of the uppermost part of a sample, / .e., surface layer. Therefore, all elements measured by XPS are contained in the surface layer.

[0083] For the surface analysis of positive electrode active material powder particles, XPS measurement is carried out using a Thermo K-a+ spectrometer. Monochromatic Al Ka radiation (hu = 1486.6 eV) is used with a spot size of 400 mm and measurement angle of 45 °. A wide survey scan to identify elements present at the surface is conducted at 200 eV pass energy. Cis peak having a maximum intensity (or centered) at a binding energy of 284.8 eV is used as a calibrate peak position after data collection. Accurate narrow scans are performed afterwards at 50 eV for at least 10 scans for each identified element to determine the precise surface composition.

[0084] Curve fitting is done with CasaXPS Version2.3.19PR1.0 using a Shirley-type background treatment and Scofield sensitivity factors. The fitting parameters are according to Table la. Line shape GL(30) is the Gaussian / Lorentzian product formula with 70% Gaussian line and 30% Lorentzian line. Table la. XPS fitting parameter for Ni2p, Mn2p, Co2p, AI2p, Bls, and W4f.

[0085] For Ni, Al, and W peaks, constraints are set for each defined peak according to Table lb. The area of Ni2p3 peakl and the area of Ni2p3 peak2 from the fitted peaks of Ni are correlated to Ni2+and Ni3+, respectively.

[0086] Table lb. XPS fitting constraints for Ni, Al, and W peak fitting.

[0087] The Al, B, and W surface contents as determined by XPS are expressed as atomic fractions of

[0088] Al, B, and W, respectively, in the surface layer of the particles divided by the total content of

[0089] Ni, Mn, Co, Al, B, and W in said surface layer. It is calculated as follows:

[0090] Al (at%) atomic ratio of Al to Ni,Mn, Co,Al,B, and W by XPS = AlXPS

[0091] Ni+Mn+Co+Al+B + W (at%)

[0092] B (at%) atomic ratio of B to Ni, Mn, Co, Al, B, and W by XPS = BXPS=

[0093] Ni + Mn + Co+Al + B + W (at%)

[0094] W (at%) atomic ratio of W to Ni,Mn,Co,Al,B,and W by XPS = WXPS=

[0095] Ni+Mn + Co + Al+B + W (at%)

[0096] C) Coin cell testing

[0097] C-l) Coin cell preparation

[0098] For the preparation of a positive electrode, a slurry that contains a positive electrode active material powder, conductor (Super P, Timcal), binder (KF#9305, Kureha) - with a formulation of 96.5: 1.5:2.0 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 170 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 and a piece of lithium foil used as a negative electrode. IM LiPFe in EC / DMC (1 :2) is used as electrolyte and is dropped between separator and electrodes. Then, the coin cell is completely sealed to prevent leakage of the electrolyte.

[0099] C-2) Testing method

[0100] The testing method is a conventional "constant cut-off voltage" test. The conventional coin cell test in the present invention follows the schedule shown in Table 2. Each cell is cycled at 25 °C using a Toscat-3100 computer-controlled galvanostatic cycling station (from Toyo).

[0101] The schedule uses a 1C current definition of 220 mA / g in the 4.3 V to 3.0 V / Li metal window range. The capacity fading rate (QF) is obtained according to the following equation below wherein DQ1 is the discharge capacity at the first cycle.

[0102] QF (% / 100 cycles) = 100 100

[0103] Table 2. Cycling schedule for coin cell testing method D) Full cell testing

[0104] D-l) Full cell preparation

[0105] 2000 mAh pouch-type cells are prepared as follows: : the positive electrode active material powder, Super-P (Super-P, Imerys Graphite & Carbon) as positive electrode conductive agents, and polyvinylidene fluoride (PVDF S5130, Solvay) as a positive electrode binder are added to N-methyl-2-pyrrolidone (NMP) as a dispersion medium so that the mass ratio of the positive electrode active material powder, the positive electrode conductive agents: super P: positive electrode binder is set at 95:3:2. Thereafter, the mixture is kneaded to prepare a positive electrode mixture slurry. The resulting positive electrode mixture slurry is then applied onto both sides of a positive electrode current collector, made of a 20 pm thick aluminum foil. The width of the applied area is 88.5 mm and the length is 425 mm. Typical loading weight of a positive electrode active material is about 14.8±1 mg / cm2. The electrode is then dried and calendared using a pressure of 4.5 MPa. In addition, an aluminum plate serving as a positive electrode current collector tab is arc-welded to an end portion of the positive electrode.

[0106] Commercially available negative electrodes are used. In short, a mixture of artificial graphite, carbon (Super P (Imerys)), carboxy-methyl-cellulose-sodium, and styrene-butadiene-rubber, in a mass ratio of 95.0 / 1 / 1.5 / 2.5, is applied on both sides of a copper foil. A nickel plate serving as a negative electrode current collector tab is arc-welded to an end portion of the negative electrode. Typical loading weight of a negative electrode active material is about 10 ± 1 mg / cm2.

[0107] Non-aqueous electrolyte is obtained by dissolving lithium hexafluorophosphate (LiPFe) salt at a concentration of 1.2 mol / L in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1 : 1: 1. It contains 1.0 wt.% lithium difluorophosphate (IJPO2F2), and 1.0 wt.% vinylene carbonate (VC) as additives.

[0108] A sheet of the positive electrode, a sheet of the negative electrode, and a sheet of the microporous polymer separator (13 pm) interposed between them are spirally wound using a winding core rod in order to obtain a spirally wound electrode assembly. The assembly and the electrolyte are then put in an aluminum laminated pouch in an air-dry room with dew point of -50°C, so that a flat pouch-type lithium secondary battery is prepared. The design capacity of the secondary battery is 2000 mAh when charged to 4.20 V. The full cell testing procedure uses a 1 C current definition of 2000 mA / g.

[0109] D-2) Cycle life test

[0110] A. Pre-charging and formation The non-aqueous electrolyte solution is impregnated into the prepared dry battery for 8 hours at room temperature. The battery is pre-charged with the current of 0.25 C until 14% of its theoretical capacity and aged for a day at room temperature. The battery is then degassed using a pressure of -760 mmHg for 30 seconds, and the aluminum pouch is sealed. During measurement, the pouch is assembled in a press jig provided with silicon pad.

[0111] The battery is charged with a current of 0.2 C in CC mode (constant current) up to 4.2 V and CV mode (constant voltage) until a cut-off current of C / 20 is reached. The battery is discharged with a current of 0.2 C in CC mode down to 2.7 V. Then, it is fully charged with a current of 0.50 C in CC mode up to 4.2 V and CV mode until a cut-off current of C / 20 is reached.

[0112] Afterwards, cell is discharged with a current of 0.50 C in CC mode down to 2.7 V. It is again charged with a current of 0.5 C in CC mode up to 4.2 V and CV mode until a cut-off current of C / 20 is reached. The final charging step is done in 25°C.

[0113] B. Bulging test

[0114] 2000 mAh pouch-type batteries prepared by above preparation method are fully charged until 4.2V and inserted in an oven which is heated to 90°C, then stays for 20 hours. At 90°C, the charged positive electrode reacts with an electrolyte and creates gas. The evolved gas creates a bulging. The increase of thickness ((thickness after storage-thickness before storage) / thickness before storage*100%) is measured after 20 hours.

[0115] C. Cycle life test

[0116] The lithium secondary full cell batteries are charged and discharged continuously under the following conditions at 25°C, to determine their charge-discharge cycle performance:

[0117] - Charge is performed in CC mode under 1 C rate up to 4.25 V, then CV mode until C / 20 is reached,

[0118] - The cell is then set to rest for 10 minutes,

[0119] - Discharge is done in CC mode at 1 C rate down to 2.7 V,

[0120] - The cell is then set to rest for 10 minutes,

[0121] - The charge-discharge cycles proceed until 600 cycles. Every 100 cycles, the discharge is done at 0.1 C rate in CC mode down to 2.7 V.

[0122] The internal resistance or direct current resistance (DCR) is measured at 1.5 C for 10 s at the beginning of every 100 cycles repetition and the end of 600th cycles.

[0123] EXAMPLES

[0124] The present invention is further illustrated in the following examples. Example 1

[0125] A positive electrode active material powder CEX1 is obtained through following steps:

[0126] 1) Preparing a first mixture: 60.0 kilograms of Nio.7sMno.25(OH)2, 0.10 kilograms of ZrC>2, 28.2 kilograms of LiOH, and 1.05 kilograms of CO3O4 are mixed homogeneously to obtain a first mixture.

[0127] 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 930 °C for 11 hours and 40 minutes to obtain a first heated material.

[0128] 3) Milling: The first heated material is milled by using a bead mill process. 60.0 kilograms of the first heated material is bead milled in 40.0 kilograms of deionized water with ZrC>2 beads to prepare a milled material. The milled material is dried at 120 °C and sieved to obtain a dried material.

[0129] 4) Preparing a second mixture: 2.2 kilograms of the dried material, 1.04 grams of AI2O3, 3.15 grams of H3BO3, and 8.32 grams of WO3 are mixed homogeneously to obtain a second mixture.

[0130] 5) Second heating: The second mixture obtained from step 4) is heated at 375 °C for 7 hours and 20 minutes to obtain a second heated material.

[0131] 6) Preparing a third mixture: 2.2 kilograms of the second heated material and 2.08 grams of AI2O3 are mixed homogeneously to obtain a third mixture.

[0132] The third mixture is sieved so as to obtain a positive electrode active material powder CEX1.

[0133] Example 1

[0134] A positive electrode active material powder EXI is obtained through following steps:

[0135] 1) Preparing a first mixture: 60.0 kilograms of Nio.7sMno.25(OH)2, 0.10 kilograms of ZrC>2, 28.2 kilograms of LiOH, and 1.05 kilograms of CO3O4 are mixed homogeneously to obtain a first mixture.

[0136] 2) First heating: The first mixture obtained from step 1) is heated in an oxygen atmosphere at 930 °C for 11 hours and 40 minutes to obtain a first heated material.

[0137] 3) Milling: The first heated material is milled by using a bead mill process. 60.0 kilograms of the first heated material is bead milled in 36.0 kilograms of deionized water with ZrC>2 beads to prepare a milled material. 177.0 grams of Al2(SO4)s is added to be dissolved in said deionized water during the bead mill. The milled material is dried at 120 °C and sieved to obtain a dried material.

[0138] 4) Preparing a second mixture: 2.2 kilograms of the dried material, 3.15 grams of H3BO3, and 8.32 grams of WO3 are mixed homogeneously to obtain a second mixture.

[0139] 5) Second heating: The second mixture obtained from step 4) is heated at 375 °C for 7 hours and 20 minutes to obtain a second heated material.

[0140] 6) Preparing a third mixture: 2.2 kilograms of the second heated material and 2.08 grams of AI2O3 are mixed homogeneously to obtain a third mixture. The third mixture is sieved so as to obtain a positive electrode active material powder EXI.

[0141] Comparative Example 2

[0142] A positive electrode active material powder CEX2 is prepared according to the same method as CEX1 except that 2.08 grams of AI2O3 is used in step 4) instead of using 1.04 grams of AI2O3.

[0143] Example 2

[0144] A positive electrode active material powder EX2 is prepared according to the same method as EXI except that 354.0 grams of Al2(SO4)s is used in step 3) instead of using 177.0 grams of AI2(SO4)3.

[0145] Comparative Example 3

[0146] A positive electrode active material powder CEX3 is prepared according to the same method as CEX1 except that 4.16 grams of AI2O3 is used in step 4) instead of using 1.04 grams of AI2O3.

[0147] Example 3

[0148] A positive electrode active material powder EX3 is prepared according to the same method as EXI except that 708.0 grams of Al2(SO4)s is used in step 3) instead of using 177.0 grams of AI2(SO4)3.

[0149] able 3. Summary of the ICP-OES and XPS results for the examples and the comparative examples The atomic ratio of Li / Me was 1.03, where Me is Ni, Mn, Co, Al, B, and W. The atomic contents were in at% relative to total contents of Ni, Mn, Co, Al, B, and W. * AIXPS, BXPS, and WXPS are the contents of Al, B, and W in at%, respectively, with respect to total amounts of Ni, Mn, Co, Al, B, and W analyze y XPS. ** AIICP, BICP, and WICP are the contents of Al, B, and W in at%, respectively, with respect to total amounts of Ni, Mn, Co, Al, B, and W analyze y ICP-OES.

[0150] Table 3 summarizes the elemental contents of the examples and comparative examples analyzed by ICP-OES and XPS. Since the XPS results are acquired from the first few nanometers (e.g. 1 nm to 10 nm) of the uppermost part of a sample, AIXPS, BXPS and WXPS represent the contents of Al, B and W, respectively, on the surface of the particle of a sample. AIICP, BICP and WICP are the contents of Al, B and W, respectively, in the entire particle of a sample.

[0151] Table 4. Summary of the electrochemical properties

[0152] Table 4 summarizes the electrochemical properties such as a capacity fading (QF, %) analyzed by coin cell test and a cycle life and DCR growth analyzed by full cell test. The cycle life is the number of cycles when the retention capacity reaches 80% of the initial capacity, and the DCR growth is the growth of DCR after 500 cycles.

[0153] Referring to Table 3, although AIICP, BICP and WICP of EXI are similar to AIICP, BICP and WICP of CEX1, AIXPS / AIICP of EXI is much higher than AIXPS / AIICP of CEX1. Likewise, although AIICP, BICP and WICP of EX2 are similar to AIICP, BICP and WICP of CEX2, AIXPS / AIICP of EX2 is much higher than AIXPS / AIICP of CEX2. Although AIICP, BICP and WICP of EX3 are similar to AIICP, BICP and WICP of CEX3, AIXPS / AIICP of EX3 is much higher than AIXPS / AIICP of CEX3. Accordingly, the particle of the positive electrode active material powder prepared by the method according to the present invention has a higher content of Al on its surface.

[0154] In addition, referring to Table 3, although AIICP, BICP and WICP of EXI are similar to AIICP, BICP and WICP of CEX1, Ni3+ / Ni2+of EXI is higher than that of CEX1. Although AIICP, BICP and WICP of EX2 are similar to AIICP, BICP and WICP of CEX2, N i3+ / N i2+of EX2 is higher than that of CEX2. Although AIICP, BICP and WICP of EX3 are similar to AIICP, BICP and WICP of CEX3, N i3+ / N i2+of EX3 is higher than that of CEX3. Since the more Ni2+is formed, the likelihood of cation mixing increases. The cation mixing affects the electrochemical performance of lithium-ion rechargeable batteries. Table 2 also demonstrates that the capacity fading (QF) of EXI, which is analyzed by coin cell test, is improved compared to that of CEX1, and the cycle life and the DCR growth of EXI, which are analyzed by full cell test, are much improved compared to those of CEX1. Likewise, QF, the cycle life, and the DCR growth of EX2 are improved compared to those of CEX2, and QF, the cycle life, and the DCR growth of EX3 are improved compared to those of CEX3. Thus, the positive electrode active material powder prepared by the method according to the present invention has a higher Ni3+ / Ni2+, which results in the decrease of cation mixing and the improvement of the electrochemical properties such as QF, cycle life, and DCR growth.

[0155] Accordingly, it is obviously observed that the positive electrode active material prepared by the method according to the present invention has Ni3+ / Ni2+of at least 1.45, and it can achieve the object of the present invention, which is to provide a positive electrode active material powder comprising Al to improve the performance of the battery comprising the positive electrode active material powder, in particular longer cycle life and lower DCR growth.

Claims

CLAIMS1. A positive electrode active material powder for lithium-ion rechargeable batteries, wherein the positive electrode active material powder comprises particles, wherein each of the particles consists of at least one primary particle and at most twenty primary particles, wherein the positive electrode active material powder comprises Li, M', and O, wherein M' comprises:- Ni in a content x, wherein 45.0 at% < x < 95.0 at%, relative to M',- Mn in a content y, wherein 0.0 at% < y < 30.0 at%, relative to M',- Co in a content z, wherein 0.0 at% < z < 20.0 at%, relative to M',- D in a content a, wherein 0.0 at% < a < 2.0 at%, relative to M', wherein D comprises at least one element selected from Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, Zn, and Zr, and- Al in a content b, wherein 0.00 at% < b < 1.00 at%, relative to M',- B in a content c, wherein 0.00 at% < c < 1.00 at%, relative to M', and- W in a content d, wherein 0.00 at% < d < 1.00 at%, relative to M', wherein x, y, z, a, b, c, and d are measured by ICP-OES, wherein x+y+z+a + b+c+d is 100.0 at%, and wherein a ratio of Ni3+to Ni2+of the positive electrode active material powder as measured by X-ray Photoelectron Spectroscopy (XPS) is at least 1.45, preferably at least 1.50, more preferably at least 1.60, most preferably at least 1.65.

2. The positive electrode active material powder according to claim 1, wherein AIXPS / AIICP > 101.0, AIXPS being a content of Al in at% relative to M', as measured by XPS analysis, and AIICP being a content of Al in at% relative to M', as measured by ICP-OES, preferably AIXPS / AIICP > 105.0.

3. The positive electrode active material powder according to claim 1 or 2, wherein BXPS / BICP > 100.0, BXPS being a content of B in at% relative to M', as measured by XPS analysis, and BICP being a content of B in at% relative to M', as measured by ICP-OES.

4. The positive electrode active material powder according to any of the preceding claims, wherein WXPS / WICP > 10.0, WXPS being a content of W in at% relative to M', as measured by XPS analysis, and WICP being a content of W in at% relative to M', as measured by ICP-OES.

5. The positive electrode active material powder according to any of the preceding claims, wherein WXPS / WICP < 28.0, WXPS being a content of W in at% relative to M', as measured by XPS analysis, and WICP being a content of W in at% relative to M', as measured by ICP-OES.

6. The positive electrode active material powder according to any of the preceding claims, wherein 70.0 at% < x < 80.0 at%, preferably 72.0 at% < x < 78.0 at%, more preferably x is about 75.0 at%.

7. The positive electrode active material powder according to any of the preceding claims, wherein 20.0 at% < y < 30.0 at%, preferably 22.5 at% < y < 27.5 at%, more preferably y is about 25.0 at%.

8. The positive electrode active material powder according to any of the preceding claims, wherein 0.0 at% < z < 5.0 at%, preferably 0.0 at% < z < 3.0 at%, more preferably z is 0.0 at%.

9. The positive electrode active material powder according to any of the preceding claims, wherein 0.02 at% < b < 0.95 at%, preferably 0.03 at% < b < 0.93 at%, more preferably 0.04 at% < b < 0.92 at%.

10. A method for preparing the positive electrode active material powder according to any one of claims 1 to 9, comprising:Step 1) forming a first mixture comprising a Li source and a transition metal composite precursor, wherein the transition metal composite precursor comprises Ni, Mn, and, optionally, Co;Step 2) heating the first mixture at a temperature between 650 °C and 1100 °C for 5 to 20 hours to obtain a heated material;Step 3) adding the heated material to an aqueous solution comprising a Al-containing compound, and milling the heated material to obtain a milled material;Step 4) drying the milled material to obtain a dried material;Step 5) mixing the dried material, a B-containing compound, and a W-containing compound to obtain a second mixture; andStep 6) heating the second mixture at a temperature between 250 °C and 500 °C for 2 to 15 hours to obtain the positive electrode active material powder.

11. The method according to claim 10, wherein the Al-containing compound in Step 3) is aluminum sulfate.

12. The method according to claim 10 or 11, wherein the B-containing compound in Step 5) is orthoboric acid.

13. The method according to any of claims 10 to 12, wherein the W-containing compound in Step 5) is tungsten trioxide.

14. The method according to any of claims 10 to 13, wherein the method further comprises mixing the positive electrode active material powder with alumina to form a third mixture, grinding the third mixture to form a grinded material, and sieving the grinded material.

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

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