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

Abstract

The present disclosure provides a positive electrode active material suitable for lithium-ion rechargeable batteries, comprising secondary particles comprising a plurality of primary particles, wherein the positive electrode active material comprises lithium, M', and oxygen, wherein the molar ratio of lithium to M' (Li / M') is in the range of 1.0 to 1.5, wherein M' comprises: - Ni in a content x, wherein 0 ≤ x ≤ 50 mol%, relative to M', - Mn in a content y, wherein 49 ≤ y ≤ 90 mol%, relative to M', - Co in a content z, wherein 0 ≤ z ≤ 40 mol%, relative to M', - S in a content a, wherein 0.2 < a ≤ 5 mol%, relative to M', - D in a content c, wherein 0 ≤ c ≤ 2 mol%, relative to M', wherein D is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Hf, La, Mg, Mo, Nb, Sr, Ta, Ti, V, W, Y, Zn and Zr; - wherein x, y, z, a, and c are measured by ICP-OES and x+y+z+a+c is 100 mol%; and - wherein concentration of S present between adjacent primary particles is a1 and concentration of S present in primary particles is a2 and wherein a1 / a2 > 1.

Description

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

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a lithium manganese-based oxide cathode active material for lithium-ion secondary batteries (LIBs) suitable for electric vehicle (EV) and hybrid electric vehicle (HEV) applications, a method of manufacturing said cathode active material, a battery comprising said cathode active material and the use of said battery.

[0004] BACKGROUND

[0005] Secondary batteries have become increasingly vital in modern energy storage systems, powering a wide array of devices ranging from portable electronics to electric vehicles. As the development of small and lightweight electronic products, electronic devices, communication devices and the like have advanced rapidly and a need for electric vehicles has widely emerged with respect to environmental issues, there is a demand for improvement of performance of secondary batteries used as power sources for these products. With the growing demand for high-capacity, long-lasting, and stable rechargeable batteries, there is a critical need for the development of advanced cathode materials that can meet the stringent requirements of various battery applications.

[0006] Lithium- and manganese-rich oxides are appealing in terms of safety and energy density. However, these lithium- and manganese-rich oxides must be charged above 4.5 V to reach high discharge capacities of around 250 mAh / g. This high operating potential (> 4.5 V) can pose problems for the long-term stability of these cathodes due to their unfavorable reactions with the electrolyte and dissolution of transition metals occurring at the electrodeelectrolyte interface. As a result, the cycle performance of the cathode active material can be reduced.

[0007] Therefore, there is a need to mitigate the reactions between these cathodes and electrolytes by modifying these cathodes thereby further increasing the cycle life of the cathode active materials. The electrochemical properties, stability, and specific surface area of the cathode active material are crucial factors that directly influence the overall performance and longevity of secondary batteries.

[0008] It is an object of the present disclosure to provide a positive electrode active material having one or more improved properties, such as an increased cycle performance.

[0009] It is a further object of the present disclosure to provide a method for manufacturing the positive electrode active material. It is a further object of the present disclosure to provide a battery comprising the positive electrode active material.

[0010] It is a further object of the present disclosure to provide a use of the battery.

[0011] SUMMARY

[0012] The present disclosure provides a positive electrode active material suitable for lithium-ion rechargeable batteries, comprising secondary particles comprising a plurality of primary particles, wherein the positive electrode active material comprises lithium, M', and oxygen, wherein the molar ratio of lithium to M' (Li / M') is in the range of 1.0 to 1.5, wherein M' comprises:

[0013] - Ni in a content x, wherein 0 < x < 50 mol%, relative to M',

[0014] - Mn in a content y, wherein 49 < y < 90 mol%, relative to M',

[0015] - Co in a content z, wherein 0 < z < 40 mol%, relative to M',

[0016] - S in a content a, wherein 0.2 < a < 5 mol%, relative to M',

[0017] - D in a content c, wherein 0 < c < 2 mol%, relative to M', wherein D is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Hf, La, Mg, Mo, Nb, Sr, Ta, Ti, V, W, Y, Zn and Zr;

[0018] - wherein x, y, z, a, and c are measured by ICP-OES and x+y+z+a+c is 100 mol%; and

[0019] - wherein concentration of S present between adjacent primary particles is al and concentration of S present in primary particles is a2 and wherein al / a2 > 1.

[0020] A further aspect of the present disclosure provides a method for manufacturing of the positive electrode active material, wherein said method comprises steps of:

[0021] Step 1) mixing a transition metal-based precursor with a source of Li and a source of S, Step 2) heating the mixture in an oxidizing atmosphere at a temperature between 600 °C and 1000 °C so as to obtain the positive electrode active material; and

[0022] Wherein the source of S is selected from the group consisting of Li2SC>4, Na2SC>4, NiSCk, MnSC , CoSO4, TiSO4, MgSO4, AI2(SO4)3 and WS2.

[0023] A further aspect of the present disclosure provides a battery comprising the positive electrode active material.

[0024] A further aspect of the present disclosure provides a use of the battery.

[0025] BRIEF DESCRIPTION OF THE FIGURES

[0026] Figure 1 is the HAADF image (Magnification at 28.5k and scale bar: 200nm) and the element distribution of W (W-M line at 1.78keV) and S (S-K line at 2.31 keV) of EX1.2. Figure 2 is the element distribution of W (W-M line at 1.78keV) and S (S-K line at 2.31keV) from area 1 to 6.

[0027] Figure 3 is the normalized element contents of figure 3 in at% relative to total contents of Ni, Mn, Co, W and S.

[0028] DETAILED DESCRIPTION

[0029] 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. On the contrary, the invention includes numerous alternatives, modifications, and equivalents as will become apparent from consideration of the following detailed description and accompanying drawings. Furthermore, where feasible, each element of the described alternatives, modifications, and equivalents may be combined with any other element of the alternatives, modifications, or equivalents.

[0030] 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".

[0031] A positive electrode active material is defined as a material which is electrochemically active in a positive electrode. By active material, it must be understood a material capable of capturing and releasing Li ions when subjected to a voltage change over a predetermined period of time.

[0032] In the framework of the present disclosure, mol% signifies molar percentage. The mol% or "mol percent" of a given element expression of a concentration means how many percent of all atoms in the concerned compound are atoms of said element. The designation mol% is equivalent to at% or atomic percent.

[0033] Positive electrode active material

[0034] The present disclosure provides a positive electrode active material suitable for lithium-ion rechargeable batteries, comprising secondary particles comprising a plurality of primary particles, wherein the positive electrode active material comprises lithium, M', and oxygen, wherein the molar ratio of lithium to M' (Li / M') is in the range of 1.0 to 1.5, wherein M' comprises:

[0035] - Ni in a content x, wherein 0 < x < 50 mol%, relative to M',

[0036] - Mn in a content y, wherein 49 < y < 90 mol%, relative to M',

[0037] - Co in a content z, wherein 0 < z < 40 mol%, relative to M',

[0038] - S in a content a, wherein 0.2 < a < 5 mol%, relative to M',

[0039] - D in a content c, wherein 0 < c < 2 mol%, relative to M', wherein D is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Hf, La, Mg, Mo, Nb, Sr, Ta, Ti, V, W, Y, Zn and Zr;

[0040] - wherein x, y, z, a, and c are measured by ICP-OES and x+y+z+a+c is 100 mol%; and

[0041] - wherein concentration of S present between adjacent primary particles is al and concentration of S present in primary particles is a2 and wherein al / a2 > 1.

[0042] There could be space (and / or pores) between adjacent primary particles, and space may include intraparticle pore(s), or may be deemed as intraparticle pore(s). Preferably, S exists in primary particles and between adjacent primary particles. Preferably concentration of S present between adjacent primary particles (a'l) is higher than concentration of S present in primary particles (a'2). Preferably, concentration ratio (a'l / a'2) of S present between adjacent primary particles (a'l) and S present in primary particles (a'2) is more than 1, preferably more than 2, preferably more than 3, preferably more than 5, more preferably more than 10.

[0043] Preferably, the Ni content x is 0 mol% or more than 0 mol% relative to M', preferably more than 10 mol% relative to M', more preferably more than 20 mol% relative to M'. Preferably, the Ni content x is less than 50 mol% relative to M', preferably less than 45 mol% relative to M', more preferably less than 40 mol% relative to M'. Preferably, the Ni content x is in the range of 0 < x < 50 mol% relative to M', preferably, in the range of 10 < x < 45 mol% relative to M', more preferably, in the range of 20 < x < 40 mol% relative to M'.

[0044] Preferably, the Mn content y is more than 49 mol% relative to M', preferably more than 50 mol% relative to M', more preferably more than 55 mol% relative to M'. Preferably, the Mn content y is less than 90 mol% relative to M', preferably less than 85 mol% relative to M', more preferably less than 80 mol% relative to M'. Preferably, the Mn content y is in the range of 49 < y < 90 mol% relative to M', preferably, in the range of 50 < y < 85 mol% relative to M', more preferably, in the range of 55 < y < 80 mol% relative to M'.

[0045] Preferably, the Co content z is 0 mol% or more than 0 mol% relative to M'. Preferably, the Co content z is less than 40 mol% relative to M', preferably less than 20 mol% relative to M', more preferably less than 10 mol% relative to M'. Preferably, the Co content z is in the range of 0 < z < 40 mol% relative to M', preferably, in the range of 0 < z < 20 mol% relative to M', more preferably, in the range of 0 < z < 10 mol% relative to M'.

[0046] Preferably, the S content a is more than 0.2 mol% relative to M', preferably more than 0.3 mol% relative to M', preferably more than 0.4 mol% relative to M', preferably more than 0.5 mol% relative to M', preferably more than 0.6 mol% relative to M', preferably more than 0.7 mol% relative to M', more preferably more than 0.8 mol% relative to M'. Preferably, the S content a is less than 5 mol% relative to M', preferably less than 4.5 mol% relative to M', preferably less than 4 mol% relative to M', preferably less than 3.5 mol% relative to M', preferably less than 3.3 mol% relative to M', more preferably less than 3 mol% relative to M'. Preferably, the S content a is in the range of 0.2 < a < 5 mol% relative to M', preferably, in the range of 0.3 < a < 4.5 mol% relative to M', preferably, in the range of 0.4 < a < 4 mol% relative to M', preferably, in the range of 0.5 < a < 3.5 mol% relative to M', preferably, in the range of 0.6 < a < 3.3 mol% relative to M', preferably, in the range of 0.7 < a < 3 mol% relative to M', more preferably, in the range of 0.8 < a < 3 mol% relative to M'.

[0047] Preferably, concentration ratio (xl / al) of Ni present between adjacent primary particles (xl) and S present between adjacent primary particles (al) is less than 1, preferably less than 0.9, preferably less than 0.8, preferably less than 0.7, preferably less than 0.6, preferably less than 0.5, preferably less than 0.4, more preferably less than 0.3.

[0048] Preferably, concentration ratio (yl / al) of Mn present between adjacent primary particles (yl) and S present between adjacent primary particles (al) is less than 1, preferably less than 0.9, preferably less than 0.8, preferably less than 0.7, preferably less than 0.6, preferably less than 0.5, preferably less than 0.4, more preferably less than 0.3.

[0049] Preferably, concentration ratio (zl / al) of Co present between adjacent primary particles (zl) and S present between adjacent primary particles (al) is less than 1, preferably less than 0.9, preferably less than 0.8, preferably less than 0.7, preferably less than 0.6, preferably less than 0.5, preferably less than 0.4, more preferably less than 0.3.

[0050] There could be space (and / or pores) between adjacent secondary particles, and space may include interparticle pore(s), or may be deemed as interparticle pore(s). Preferably, S exists between adjacent primary particles and between adjacent secondary particles. Preferably concentration of S present between adjacent primary particles (al) is higher than concentration of S present between adjacent secondary particles (a3). Preferably, concentration ratio (a3 / al) of S present between adjacent secondary particles (a3) and S present between adjacent primary particles (al) is less than 1, preferably less than 0.95, more preferably less than 0.9.

[0051] The positive electrode active material of the present disclosure may comprise impurities or be doped or coated resulting in an overall positive electrode active material comprising one or more elements other than Li, Ni, Mn, Co, S and O, which is reflected in the parameter "D" used herein. In an embodiment the positive electrode active material comprises D, wherein D is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Hf, La, Mg, Mo, Nb, Sr, Ta, Ti, V, W, Y, Zn and Zr; preferably Al, Ti, Cr, Nb, Sr, Y, Zr and W; more preferably Al, Ti, Nb, Zr and W.

[0052] A preferred embodiment is the positive electrode active material according to the present disclosure, wherein D is in content c > 0 mol%, preferably c > 0.25 mol%, preferably c > 0.5 mol%. In a preferred embodiment the content c < 5 mol%, preferably c < 4 mol%, more preferably c < 2 mol%. In a preferred embodiment the content is 0 < c < 5 mol%, preferably 0.25 mol% < c < 4 mol%, preferably 0.5 < c < 2 mol%.

[0053] In a preferred embodiment the molar ratio of Li to M' (mol / mol) is more than 0.9, preferably more than 1, more preferably more than 1.1. In a preferred embodiment the molar ratio of Li to M' (mol / mol) is less than 1.8, preferably less than 1.7, more preferably less than 1.6. In a preferred embodiment the molar ratio of Li to M' (mol / mol) is between 0.9 and 1.8, preferably between 1 and 1.7, preferably between 1 and 1.6, preferably between 1 and 1.5, preferably between 1.1 and 1.4, preferably between 1.1 and 1.3, more preferably between 1.2 and 1.3.

[0054] As appreciated by the skilled person the amount of Li, Ni, Mn, Co, S, W and others measured with Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). For example, but not limiting to the invention, an Agilent ICP 720-ES is used in the ICP-OES analysis. In the framework of the present invention, "atomic content" of a given element expression of a concentration means how many percent of all atoms in the concerned compound are atoms of said element. The designation mol% is equivalent to "molar percent" or "at%". For example, but not limiting to the invention, XPS analysis is carried out with a Thermo K-o+ spectrometer (Thermo Scientific).

[0055] Method for Preparing Positive Electrode Active Material

[0056] Hereinafter, a method for preparing a positive electrode active material according to an embodiment of the present disclosure will be described in detail. A positive electrode active material is prepared according to the following steps. First, a step of forming precursor particles is performed. As a more preferable example, the precursor particles may be manufactured by co-precipitation, and a complexing agent may be added for the manufacturing.

[0057] Then, a step of mixing a lithium compound with the precursor particles in an industrial blender to obtain a mixture having a lithium to metal molar ratio from 0.9 to 1.8 is performed. In a preferred embodiment the molar ratio of a lithium to metal is more than 0.9, preferably more than 1, more preferably more than 1.1. In a preferred embodiment the molar ratio of a lithium to metal is less than 1.8, preferably less than 1.7, more preferably less than 1.6. In a preferred embodiment the molar ratio of a lithium to metal is between 0.9 and 1.8, preferably between 1 and 1.7, preferably between 1 and 1.6, preferably between 1 and 1.5, preferably between 1.1 and 1.4, preferably between 1.1 and 1.3, more preferably between 1.2 and 1.3.

[0058] Then, a step of heating the mixture at 600 °C to 1000 °C followed by cooling is performed. In a preferred embodiment heating temperature is between 650 °C to 1000 °C, preferably between 700 °C to 950 °C, preferably between 750 °C to 900 °C, more preferably between 870 °C to 900 °C.

[0059] An embodiment of the present disclosure may include S or W or the combination thereof as coating material or dopant in the positive electrode active material.

[0060] In a preferred embodiment the S content is more than 0 mol%, preferably more than 0.2 mol%, preferably more than 0.3 mol%, preferably more than 0.4 mol%, preferably more than 0.5 mol%, preferably more than 0.6 mol%, preferably more than 0.7 mol%, more preferably more than 0.8 mol%. Preferably, the S content is less than 5 mol%, preferably less than 4.5 mol%, preferably less than 4 mol%, preferably less than 3.5 mol%, preferably less than 3.3 mol%, more preferably less than 3 mol%. Preferably, the S content is in the range of 0 < S < 5 mol%, preferably, in the range of 0.2 < S < 4.5 mol%, preferably, in the range of 0.3 < S < 4 mol%, preferably, in the range of 0.4 < S < 3.5 mol%, preferably, in the range of 0.5 < S < 3.5 mol%, preferably, in the range of 0.6 < S < 3.5 mol%, preferably, in the range of 0.7 < S < 3 mol%, more preferably, in the range of 0.8 < S < 3 mol%.

[0061] In a preferred embodiment the source of S is selected from the group consisting of IJ2SO4, Na2SO4, NiSO4, MnSO4, CoSO4, TiSO4, MgSO4, AI2(SO4)3and WS2.

[0062] In a preferred embodiment the W content is 0 mol% or more than 0 mol%, preferably more than 0.05 mol%, preferably more than 0.1 mol%, preferably more than 0.15 mol%, preferably more than 0.17 mol%, more preferably more than 0.2 mol%. Preferably, the W content is less than 3 mol%, preferably less than 2.5 mol%, preferably less than 2 mol%, preferably less than 1.7 mol%, more preferably less than 1.5 mol%,. Preferably, the W content is in the range of 0 < W < 3 mol%, preferably, in the range of 0.05 < W < 2.5 mol%, preferably, in the range of 0.1 < W < 2 mol%, preferably, in the range of 0.15 < W < 1.7 mol%, preferably, in the range of 0.17 < W < 1.5 mol%, more preferably, in the range of 0.2 < W < 1.5 mol%.

[0063] In a preferred embodiment the source of W is selected from the group consisting of WO3, U2WO4, Na2WO4, H2WO4 and WS2.

[0064] An embodiment of the present disclosure may include a step of subjecting the precursor particles to wet coating or dry coating with a compound containing at least one element selected from the group consisting of Al, B, Ba, Ce, Fe, La, Mg, Mo, Nb, Sr, Ti, V, Cr, Ca, Nb, Mo, Hf, Ta, Y, Zn and Zr, after the step of forming precursor particles, and before the step of heating.

[0065] Battery

[0066] The present disclosure provides a battery comprising the positive electrode active material. In a preferred embodiment the battery is a lithium-ion battery, preferably a lithium-ion rechargeable battery. The battery according to an embodiment of the present disclosure includes the positive electrode active material, a binder, a conductor, and a solvent. The positive electrode active material is as described above, and a binder, a conductor, and a solvent are not particularly limited as long as these can be used on a cathode current collector for a secondary battery.

[0067] Use

[0068] The present disclosure provides a use of the positive electrode active material. A preferred embodiment is the use of the positive electrode active material in a battery, to increase the efficiency of the battery. Furthermore, the present disclosure provides a use of the battery in either one of a portable computer, a tablet, a mobile phone, an energy storage system (ESS), an electric vehicle (EV) or in a hybrid electric vehicle (HEV), preferably in an electric vehicle or in a hybrid electric vehicle that includes the positive electrode active material according to the disclosure.

[0069] EXAMPLES

[0070] Hereinafter, positive electrode active materials according to examples of the present disclosure are specifically described. Comparative Example 1

[0071] A positive electrode active material, further called CEX1, is prepared according to the following steps:

[0072] Step 1) Co-precipitation: a transition metal-based precursor A with metal composition of Ni0.34Mn0.57Co0.09 is prepared with mixed nickel-manganese-cobalt sulfates, sodium hydroxide, and ammonia. The transition metal-based precursor A has D50 of 6.7 pm and specific surface area of 14.6 m2 / g.

[0073] Step 2) Mixing: the transition metal-based precursor A is mixed with LiOH in an industrial blender to obtain a mixture having a lithium to metal (Ni, Mn, and Co) molar ratio of 1.26. Step 3) Heating: the mixture is heated at 875 °C for 10 hours in an oxidizing atmosphere. The heated powder is crushed, classified, and sieved to obtain CEX1.

[0074] Example 1.1

[0075] EX1.1 is prepared according to the same method as CEX1, except that WS2 powder is added in the Step 2) together with LiOH to obtain a mixture having 0.32 mol% W relative to the total amount of Ni, Mn, and Co.

[0076] Example 1.2

[0077] EX1.2 is prepared according to the same method as CEX1, except that WS2 powder is added in the Step 2) together with LiOH to obtain a mixture having 0.47 mol% W relative to the total amount of Ni, Mn, and Co.

[0078] Example 1.3

[0079] EX1.3 is prepared according to the same method as CEX1, except that WS2 powder is added in the Step 2) together with LiOH to obtain a mixture having 0.63 mol% W relative to Ni, Mn, and Co.

[0080] Example 1.4

[0081] EX1.4 is prepared according to the same method as CEX1, except that WS2 powder is added in the Step 2) together with LiOH to obtain a mixture having 0.90 mol% W relative to Ni, Mn, and Co.

[0082] Comparative Example 2

[0083] A positive electrode active material, further called CEX2, is prepared according to the following steps:

[0084] Step 1) Co-precipitation: a transition metal-based precursor B with metal composition of Ni0.34Mn0.57Co0.09 is prepared with mixed nickel-manganese-cobalt sulfates, sodium hydroxide, and ammonia. The transition metal-based precursor B has D50 of 6.9 pm and specific surface area of 18.5 m2 / g.

[0085] Step 2) Mixing: the transition metal-based precursor B is mixed with LiOH in an industrial blender to obtain a mixture having a lithium to metal (Ni, Mn, and Co) molar ratio of 1.26. Step 3) Heating: the mixture is heated at 875 °C for 10 hours in an oxidizing atmosphere. The heated powder is crushed, classified, and sieved to obtain CEX2.

[0086] Example 2.1

[0087] EX2.1 is prepared according to the same method as CEX2, except that WS2 powder is added in the Step 2) together with LiOH to obtain a mixture having 0.19 mol% W relative to the total amount of Ni, Mn, and Co.

[0088] Example 2.2

[0089] EX2.2 is prepared according to the same method as CEX2, except that WS2 powder is added in the Step 2) together with LiOH to obtain a mixture having 0.47 mol% W relative to the total amount of Ni, Mn, and Co.

[0090] EXPERIMENTAL TESTS USED IN THE EXAMPLES

[0091] The following analysis methods are used in the Examples:

[0092] A) Particle size distribution (PSD) analysis

[0093] The particle size distribution (PSD) of the positive electrode active material powder is measured by laser diffraction particle size analysis using a Malvern Mastersizer 3000 with a Hydro MV wet dispersion accessory after having dispersed each of the powder samples in an aqueous medium. To improve the dispersion of the powder, 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 obtained from the Malvern Mastersizer 3000 with Hydro MV measurements.

[0094] B) Inductively coupled plasma - optical emission analysis (ICP-OES) analysis

[0095] The positive electrode active material examples as described herein are measured by the Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) method using an Agillent ICP 720-OES. 1 g 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 Ni, Mn, Co, W, and S are expressed as at% of the total of these contents.

[0096] C) Specific surface area analysis

[0097] The specific surface area of the positive electrode active material is measured with the Brunauer-Emmett-Teller (BET) method by using a Micromeritics Tristar II 3020. A powder sample is heated at 300 °C under a nitrogen (N2) gas for 1 hour prior to the measurement in order to remove adsorbed species. The dried powder is put into the sample tube. The sample is then de-gassed at 30 °C for 10 minutes. The instrument performs the nitrogen adsorption test at 77 K. By obtaining the nitrogen isothermal absorption / desorption curve, the total specific surface area of the sample in m2 / g is derived.

[0098] D) Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive X- ray Spectroscopy (EDS) measurement

[0099] To prepare a lamella for cross-sectional Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive X-ray Spectroscopy (EDS), the positive electrode active material particle sample is coated with 25 nm layer of carbon (Leica EM ACE600 coater) before Focused Ion Beam (FIB) preparation. FIB lamella is prepared on a Cu Omniprobe TEM grid, using a Thermo Fisher Helios FIB-SEM with Ga ion beam first at 30 kV, then at 8 kV and at the final thinning step at 2 kV and 39 pA. The lamella thickness is about 50-100 nm.

[0100] The lamella is transferred to the Ar filled glove box in the vacuum transfer box. The TEM vacuum transfer holder (Gatan) is assembled in the glove box. The High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM) and Energy Dispersive X- ray spectroscopy (EDS) are performed on an aberration corrected FEI Titan transmission electron microscope at 300 kV, using a Super X detector. The screen current is 150 pA with acquisition time of 20 min in the map size of 570x570 nm.

[0101] For EDX map scans acquisition and data processing, Esprit Quantax software version 1.9, Bruker, is used. Following elements are considered: Ni (Ni-K line at 7.47 keV), Mn (Mn-K line at 5.90 keV), Co (Co-K line at 6.93 keV), S (S-K line at 2.31 keV) and W (W-M line at 1.78 keV).

[0102] E) Coin cell testing

[0103] El) Coin cell preparation

[0104] For the preparation of a positive electrode, a slurry that contains a positive electrode active material powder, conductor (Super P, Timcal), binder (S5130, Kureha) - with a formulation of 83.0:8.0:8.0 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 230 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.

[0105] E2) Testing method

[0106] 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 1. Each cell is cycled at 25 °C using a Toscat-3100 computer-controlled galvanostatic cycling station (from Toyo). The schedule uses a 1C current definition of 160 mA / g in the 4.6 V to 2.0 V / Li metal window range. The rate performance at 0.05C, 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C is expressed as the ratio between the retained discharge capacity DQm, with m = 2, 3, 4, 5, 6, and 7 for respectively nC=0.05C, 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C as follows:

[0107] DQm nC - rate (%) = x 100

[0108] For example, 3C - rate (%) = x 100 , wherein DQ is the discharge capacity at the first cycle, and DQ7 is the discharge capacity at the 7thcycle.

[0109] Table 1. Cycling schedule for Coin cell testing method

[0110] Results

[0111] Table 2. Summary of the properties of examples and comparative examples

[0112] * The atomic contents are in at% relative to total contents of Ni, Mn, Co, W and S.

[0113] Table 2 summarizes the precursor source and additional reagent(s) of examples and comparative examples, and their corresponding ICP-OES results and electrochemical results.

[0114] EX1.1, EX1.2, EX1.3, and EX1.4 are the positive electrode active materials treated by addition of WS2. The content of S in the positive electrode active material is confirmed by ICP-OES. EX1.1 comprises 0.32 at% of W and 1.21 at% of S while CEX1 comprises 0.56 at% S without W, relative to total amount of Ni, Mn, Co, W and S. It is represented that the rate performance of a EX1.1 is 79.5 % which is higher than the rate performance of CEX1 as 70.2 %, measured by coin cell test. As well as EX1.1, the positive electrode active material EX1.2, EX1.3, and EX1.4 comprise 0.46 at%, 0.62 at%, and 0.86 at% of W respectively, and comprise 1.47 at%, 1.77 at%, and 2.96 at% of S respectively, relative to total amount of Ni, Mn, Co, W and S. The rate performance values of EX1.2, EX1.3, and EX1.4 are 78.9 %, 76.1 %, and 71.2 % respectively, which are higher than the rate performance of CEX1.

[0115] EX2.1 and EX2.2 are the positive electrode active materials treated by addition of WS2. EX2.1 and EX2.2 comprise 0.20 at% and 0.50 at% of W and 0.82 at% and 1.40 at% of S while CEX2 does not comprise W and comprise 0.44 at% of S respectively, relative to total amount of Ni, Mn, Co, W and S. It is observed that the rate performance of EX2.1 and EX2.2 are 85.5 % and 85.8 %, which are higher than the rate performance of CEX2 as 81.4 %.

[0116] Figure 1 shows the HAADF image of EX1.2 and the element distribution of S and W in EX1.2 measured by STEM-EDX mapping. It is observed that S is distributed between the adjacent primary particles of the secondary particle in EX1.2. It is clearly shown that W presents more in the primary particles and / or at the primary particles (especially in grain boundaries) than between the adjacent primary particles.

[0117] Figure 2 shows the element distribution measured by STEM-EDX mapping from the area 1 to 6 of the positive electrode active material comprising 1.2 mol% W and 2.3 mol% S and Figure 3 shows the normalized element contents in at% relative to total contents of Ni, Mn, Co, W and S. In area 1 and 2, which is space between adjacent primary particles, the normalized S content is 72.4 at% and 69.2 at%, relative to total amount of Ni, Mn, Co, W, and S and it is observed that S is mainly distributed between adjacent primary particles of the secondary particle. In area 3 to 6, which is in the primary particles, the normalized S content in area 3 to 6 is 0.4 at%, 0.2 at%, 0.9 at% and 0.4 at% respectively, relative to total amount of Ni, Mn, Co, W, and S.

Claims

CLAIMS1. A positive electrode active material suitable for lithium-ion rechargeable batteries, comprising secondary particles comprising a plurality of primary particles, wherein the positive electrode active material comprises lithium, M', and oxygen, wherein the molar ratio of lithium to M' (Li / M') is in the range of 1.0 to 1.5, wherein M' comprises:- Ni in a content x, wherein 0 < x < 50 mol%, relative to M',- Mn in a content y, wherein 49 < y < 90 mol%, relative to M',- Co in a content z, wherein 0 < z < 40 mol%, relative to M',- S in a content a, wherein 0.2 < a < 5 mol%, relative to M',- D in a content c, wherein 0 < c < 2 mol%, relative to M', wherein D is at least one element selected from the group consisting of Al, B, Ba, Ca, Ce, Cr, Fe, Hf, La, Mg, Mo, Nb, Sr, Ta, Ti, V, W, Y, Zn and Zr;- wherein x, y, z, a, and c are measured by ICP-OES and x+y+z+a+c is 100 mol%; and- wherein concentration of S present between adjacent primary particles is al and concentration of S present in primary particles is a2 and wherein al / a2 > 1.

2. The positive electrode active material according to claim 1, wherein 20 < x < 40 mol% and 55 < y < 80 mol%.

3. The positive electrode active material according to any of the previous claims, wherein 0 < z < 10 mol%.

4. The positive electrode active material according to any of the previous claims, wherein 0.6 < a < 3.3 mol%, preferably, 0.7 < a < 3 mol%, more preferably, 0.8 < a < 3 mol%5. The positive electrode active material according to any of the previous claims, wherein concentration of Ni present between adjacent primary particles is xl, and wherein xl / al < 1.

6. The positive electrode active material according to any of the previous claims, wherein concentration of Mn present between adjacent primary particles is yl, and wherein yl / al < 1.

7. The positive electrode active material according to any of the previous claims, wherein concentration of Co present between adjacent primary particles is zl, and wherein zl / al < 1.

8. The positive electrode active material according to any of the previous claims, wherein al / a2 > 2, preferably al / a2 > 3, preferably al / a2 > 5, more preferably al / a2 > 10.

9. The positive electrode active material according to any of the previous claims, wherein concentration of S present between adjacent secondary particles is a3, and wherein a3 / al < 1.

10. A method for preparing a positive electrode active material according to any of the previous claims, wherein the method comprises steps of:Step 1) mixing a transition metal-based precursor with a source of Li and a source of S,Step 2) heating the mixture in an oxidizing atmosphere at a temperature between 600 °C and 1000 °C so as to obtain the positive electrode active material; and Wherein the source of S is selected from the group consisting of Li2SC>4, Na2SC>4, NiSO4, MnSO4, CoSO4, TiSO4, MgSO4, AI2(SO4)3 and WS2.

11. The method according to claim 10, wherein the source of S is WS2.

12. The method according to claims 10 or 11, wherein the source of Li is LiOH.

13. The method according to any of the claims 10 to 12, wherein a temperature of Step 2) is between 870 °C and 900 °C.

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

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

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