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

Abstract

The present invention relates a positive electrode active material comprising lithium, oxygen, nickel, and at least one metal selected from the group consisting of manganese and cobalt, comprising Ni in a content x', wherein 40.0 ≤ x' ≤ 98.0 mol%, relative to the sum of Ni, Mn, and Co, Mn in a content y', wherein 0.0 ≤ y' ≤ 30.0 mol%, relative to the sum of Ni, Mn, and Co, Co in a content z', wherein 0.0 ≤ z' ≤ 30.0 mol%, relative to the sum of Ni, Mn, and Co, wherein the positive electrode active material has an enriched amount of silicon and boron in the surface layer. This positive electrode active material the electrochemical performance of a battery, such as the first discharge capacity and the cycling efficiency.

Description

DescriptionPositive electrode active material and method for manufacturing a positive electrode active materialTECHNICAL FIELD

[0001] The present invention relates to a positive electrode active material comprising lithium, oxygen, nickel, boron and silicon, in particular having a surface enriched in silicon and boron. This invention also relates to a method for manufacturing a positive electrode active material comprising lithium, oxygen, nickel, boron and silicon, in particular having an enriched amount of silicon and boron in the surface layer; a battery comprising said positive electrode active material and the use of said battery.BACKGROUND

[0002] As the development of small and lightweight electronic products, electronic devices, communication devices and the like has 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. Among these, a lithium secondary battery has come into the spotlight as a high-performance battery due to the high energy density and a high reference electrode potential.

[0003] During the charging process of a secondary battery, lithium ions are removed from the cathode, transported through the electrolyte and are inserted into the anode while electrons are removed from the cathode and injected into the anode through an external circuit (charger). During the use or discharge of a secondary battery lithium ions are removed from the anode, transported through the electrolyte, and are inserted into the cathode, while electrons flow through an external circuit to provide electric work.

[0004] Commonly used cathode active materials are lithium transition metal oxides. During the charging and / or discharging of the lithium battery, the delithiated cathode active material can slowly react with the non-aqueous electrolyte or the solid electrolyte leading to a gradual degradation of the electrochemical performance of lithium batteries using such cathode active materials.

[0005] It has been demonstrated that applying a surface layer on the cathode active material with metals, such as Ti or Zr, (i.e. applying a thin surface layer of the metal on thecathode active material resulting in an increased or enriched amount of said metals in the surface layer) results in a cathode active material exhibiting improved electrochemical performances as compared to their counterparts devoid of said surface layer.

[0006] Doo et al (ACS Appl. Energy Mater. 2019, 2, 6246-6253) contemplates a hydro- phobic Ni-rich oxide material obtained after mixing polycrystalline LiNiosCoo.-iMno -i with polydimethylsiloxane followed by heating at 230 °C thereby improving the electrochemical stability of the Ni-rich oxide material.

[0007] However, there remains a need to provide a positive electrode active material having an improved storage stability and / or an improved electrochemical stability.

[0008] It is an object of the present invention to provide a positive electrode active material comprising silicon and boron to improve the storage stability and / or to improve the electrochemical performance of the positive electrode active material, in particular the first discharge capacity and / or the efficiency of the reversible capacity.

[0009] It is another object of the present invention to provide a method for manufacturing a positive electrode active material comprising silicon and boron.

[0010] It is another object of the present invention to provide a battery comprising said positive electrode active material.

[0011] It is another object of the present invention to provide a use of said battery.SUMMARY OF THE INVENTION

[0012] In a first aspect an object of the invention is achieved by providing a positive electrode active material comprising lithium, oxygen, nickel, and at least one metal selected from the group consisting of manganese and cobalt, comprising a. Ni in a content x’, wherein 40.0 < x’ < 98.0 mol%, relative to the sum of Ni, Mn, and Co, b. Mn in a content y’, wherein 0.0 < y’ < 30.0 mol%, relative to the sum of Ni, Mn, and Co, c. Co in a content z’, wherein 0.0 < z’ < 30.0 mol%, relative to the sum of Ni, Mn, and Co, wherein x’, y’ and z’ are measured by ICP-OES, and wherein the positive electrode active material has an enriched amount of silicon and boron in the surface layer.

[0013] Worded differently, and as appreciated by the skilled person, the positive electrode active material of the invention has a surface layer comprising silicon and boron, in particular at amounts of Si and B that are higher than the average Si and B in the material.

[0014] The present inventors have surprisingly found that the positive electrode active material of the invention improves the electrochemical performance of the battery, in particular of a solid-state battery, such as a sulfide solid-state battery, as demonstrated in the appended examples. Specifically, the positive electrode active material of the invention increases the cycling efficiency of the battery and / or improves the first discharge capacity of the battery.

[0015] Without wishing to be bound by any theory the present inventors have found that treating the positive electrode active material with polydimethylsiloxane and boric acid results in a positive electrode active material having an enriched amount of a composition comprising silicon and boron in the surface layer of the positive electrode active material. This composition is different from the composition being present in the surface layer when the treating the positive electrode active material with silicon dioxide and boric acid. The present inventors have demonstrated this difference in composition by analyzing the positive electrode active material of the invention with XPS analysis: the positive electrode active material treated with polydimethylsiloxane and boric acid has a peak in binding energy level higher than 101 .2 eV, whereas the positive electrode active material treated with silicon dioxide and boric acid has a peak at a lower binding energy level of around 101 .2 eV. The present inventors attribute this change in binding energy level to the interaction of polydimethylsiloxane and boric acid at the surface layer of the positive electrode active material resulting in a different peak in binding energy level. As is well known by the person skilled in the art, the characteristic chemical state and surrounding environment of the atom can cause shifts in binding energy.

[0016] Moreover, the present inventors believe that the enriched amount of silicon and boron in the surface layer improves the storage stability of the positive electrode active material. In particular, a decreased uptake of water and carbon (or carbon dioxide), preferably carbon, is expected by enriching the amount of silicon and boron in the surface layer of the positive electrode active material.

[0017] Without wishing to be bound by any theory, the present inventors believe that the enriched amount of silicon and boron in the surface layer acts as a hydrophobic surfacelayer, which suppresses the formation of residual lithium compounds, such as U2CO3, which are formed due to reaction between lithium present in the positive electrode active material and water and carbon in the surrounding air, because the hydrophobic surface inhibits contact between water and the positive electrode active material.

[0018] In a further aspect the invention provides a method for manufacturing a positive electrode active material comprising lithium, oxygen, nickel, boron and silicon.

[0019] In a further aspect the invention provides a battery comprising said positive electrode active material.

[0020] In a further aspect the invention provides a use of said battery.BRIEF DESCRIPTION OF THE FIGURES

[0021] Figure 1 : XPS signal for CEX1 .2, EX1 .2 and EX2 between 98 eV and 106 eV.

[0022] Figure 2: SEM image of CEX1.1 comprising polycrystalline particles.

[0023] Figure 3: SEM image of CEX2.1 comprising single particles and secondary particles.DETAILED DESCRIPTION OF THE INVENTION

[0024] 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.

[0025] 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”.

[0026] The term “solid-state battery” as used herein and in the claims refers to a cell or a battery that includes only solid or substantially solid-state components such as solid electrodes (e.g. anode and cathode) and a solid electrolyte.

[0027] The term “a positive electrode active material” (also known as cathode active material) as used herein and in the claims is defined as a material which is electrochemically active in a positive electrode or cathode. By active material, it must be understood to be a material capable to capture and release Li ions when subjected to a voltage change over a predetermined period of time.

[0028] The term “a positive electrode” as used herein is defined as a material comprising a positive electrode active material also in addition to other components added to the positive electrode active material, which are not electrochemically active, in particular conductivity agents such as carbon black or binders such as PVDF.

[0029] In the context of the present invention the terms “solid” and “liquid” shall be considered to be a solid and liquid in standard conditions for temperature and pressure as defined by the IIIPAC, unless defined otherwise. Hereby the boiling point and the melting point shall be considered to be the boiling point and the melting point at standard atmospheric pressure, i.e. at 101325 Pa, unless specified otherwise.

[0030] In the context of the present invention the carbon content after exposure is measured through an exposure test, conducted by evenly spreading 40 grams of positive electrode active material on a 95 x 95 mm2dish and placing the dish inside a 30 °C chamber. Preferably, the atmosphere of the chamber is controlled so as to have a relative humidity level of 50%. Preferably, the positive electrode active material powder is taken for a carbon analysis by a carbon analyzer after 3 days (72 hours).

[0031] In the context of the present invention X-ray photoelectron spectroscopy (XPS) is used to analyze the surface of positive electrode active material powder particles. As appreciated by the skilled person in XPS measurement, the signal is acquired from the first few nanometers (i.e., 1 nm to 10 nm) of the uppermost part of a sample, i.e. surface layer. Worded differently, all elements measured by XPS are contained in the surface layer. Preferably, monochromatic Al Ka radiation (hu=1486.6 eV) is used with a spot size of 400 pm and measurement angle of 45 °. Preferably, a wide survey scan to identify elements present at the surface is conducted at 200 eV pass energy. Preferably, C1 s 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. Preferably, accurate narrowscans are performed afterwards at 50 eV for at least 10 scans for each identified element to determine the precise surface composition. For example but not limiting to the invention, for the surface analysis of positive electrode active material powder particles, XPS measurement is carried out using a Thermo K-a+ spectrometer. For example but not limiting to the invention, curve fitting is done with CasaXPS Version2.3.19PR1 .0 using a Shirley-type background treatment and Scofield sensitivity factors, wherein preferably line shape GL(30) is the Gaussian / Lorentzian product formula with 70% Gaussian line and 30% Lorentzian line.

[0032] In the context of the present invention the positive electrode active material of the invention having an enriched amount of silicon and / or boron in the surface layer of the positive electrode active material means that the positive electrode active material has a surface layer comprising silicon and / or boron. The presence of these enriched amounts of silicon and boron of the surface layer comprising silicon and boron is evidenced by the Sis / SiA and / or BB / BA higher than 1 , which indicates that said B and / or Si is present mostly on the surface of the positive electrode active material.Positive electrode active material

[0033] In a first aspect the present invention concerns a positive electrode active material for batteries comprising lithium, oxygen, nickel, and at least one metal selected from the group consisting of manganese and cobalt, wherein said positive electrode active material further comprises boron with a content BB, wherein BB is expressed as molar fraction of B relative to the total amount of Ni, Mn, Co, Si, and B as measured by XPS analysis, wherein BB > 0.30.

[0034] A highly preferred embodiment is the positive electrode active material of the invention for solid-state batteries.

[0035] A certain highly preferred embodiment is the positive electrode active material of the invention, wherein said positive electrode active material displays a peak in binding energy level between 101 .4 eV and 106.0 eV, as measured by XPS analysis. More preferably said positive electrode active material displays a peak in binding energy level between 101.4 eV and 105.0 eV, preferably between 101.5 eV and 104.5 eV, more preferably between 101.6 eV and 104.0 eV, as measured by XPS analysis.

[0036] A certain highly preferred embodiment is the positive electrode active material of the invention, wherein said positive electrode active material further comprises silicon.

[0037] A certain highly preferred embodiment is the positive electrode active material of the invention, wherein said positive electrode active material comprises silicon; and

[0038] wherein said positive electrode active material displays a peak in binding energy level between 101 .3 eV and 106.0 eV, as measured by XPS analysis, preferably between 101.4 eV and 106.0 eV, more preferably between 101.5 eV and 105.0 eV, most preferably between 101.6 eV and 104.0 eV, as measured by XPS analysis.

[0039] A certain preferred embodiment is the positive electrode active material of the invention, wherein said positive electrode active material comprises silicon displaying a peak in binding energy level between 101.3 eV and 106.0 eV, as measured by XPS analysis, preferably between 101.4 eV and 106.0 eV, more preferably between 101.5 eV and 105.0 eV, most preferably between 101.6 eV and 104.0 eV, as measured by XPS analysis.

[0040] A certain highly preferred embodiment is the positive electrode active material of the invention, wherein said positive electrode active material comprises silicon with a content Sis, wherein Sis is expressed as molar fraction of Si relative to the total amount of Ni, Mn, Co, Si, and B as measured by XPS analysis, and wherein Sis > 0.01 .

[0041] A certain highly preferred embodiment is the positive electrode active material of the invention, wherein said positive electrode active material comprises silicon with a content Sis, wherein Sis is expressed as molar fraction Si relative to the total amount of Ni, Mn, Co, Si, and B as measured by XPS analysis; wherein Sis > 0.01 ; and

[0042] wherein said positive electrode active material displays a peak in binding energy level between 101 .3 eV and 106.0 eV, as measured by XPS analysis, preferably between 101.4 eV and 106.0 eV, more preferably between 101.5 eV and 105.0 eV, most preferably between 101.6 eV and 104.0 eV, as measured by XPS analysis.

[0043] A preferred embodiment is the positive electrode active material of the invention having a layered structure, preferably a layered structure of the a-NaFeCh type, preferably a layered structure of the a-NaFeCh type having a R-3m space group.

[0044] A preferred embodiment is the positive electrode active material of the invention comprising Li, Ni, Mn, Co and oxygen, wherein Ni is in a content x’, wherein 50.0 < x’ < 98.0 mol%, relative to the sum of Ni, Mn and Co. A more preferred embodiment is the positive electrode active material of the invention, wherein Ni is in a content x’ > 55.0 mol%, preferably x’ > 58.0 mol%, more preferably x’ > 60.0 mol%, relative to the sum of Ni, Mn and Co. In a preferred embodiment Ni is in a content x’ < 90.0 mol% preferably x’< 88 mol%, more preferably x’ < 85.0 mol%, relative to the sum of Ni, Mn and Co. A more preferred embodiment is the positive electrode active material of the invention, wherein Ni is in a content x’ between 55.0 mol% < x’ < 90.0 mol%, preferably 58.0 mol%< x’ < 88.0 mol%, more preferably 60.0 mol% < x’ < 85.0 mol%, relative to the sum of Ni, Mn and Co.

[0045] A certain preferred embodiment is the positive electrode active material of the invention comprising Li, Ni, Mn, Co and oxygen, Ni is in a content x’ > 55.0 mol%, preferably x’ > 58.0 mol%, more preferably x’ > 60.0 mol%, relative to the sum of Ni, Mn and Co. In a certain preferred embodiment Ni is in a content x’ < 75.0 mol%, preferably x’ < 72 mol%, more preferably x’ < 70.0 mol%, relative to the sum of Ni, Mn and Co. A more certain preferred embodiment is the positive electrode active material of the invention, wherein Ni is in a content x’ between 55.0 mol% < x’ < 75.0 mol%, preferably 58.0 mol%< x’ < 72.0 mol%, more preferably 60.0 mol% < x’ < 70.0 mol%, relative to the sum of Ni, Mn and Co.

[0046] A certain preferred embodiment is the positive electrode active material of the invention comprising Li, Ni, Mn, Co and oxygen, wherein Ni is in a content x’ > 75.0 mol%, preferably x’ > 78.0 mol%, more preferably x’ > 80.0 mol%, relative to the sum of Ni, Mn and Co. In a certain preferred embodiment Ni is in a content x’ < 92.0 mol% preferably x’ < 90 mol% and more preferably x’ < 88.0 mol%, relative to the sum of Ni, Mn and Co. A more certain preferred embodiment is the positive electrode active material of the invention, wherein Ni is in a content x’ between 75.0 mol% < x’ < 92.0 mol%, preferably 78.0 mol% < x’ < 90.0 mol%, more preferably 80.0 mol% < x’ < 88.0 mol%, relative to the sum of Ni, Mn and Co.

[0047] A preferred embodiment is the positive electrode active material of the invention comprising Li, Ni, Mn, Co and oxygen, wherein Mn is in a content y’, wherein 0.0 < y’ < 30.0 mol%, relative to the sum of Ni, Mn and Co. A more preferred embodiment is the positive electrode active material of the invention, wherein Mn is in a content y’ > 0.0 mol%, preferably y’ > 1 .0 mol%, more preferably y’ > 2.0 mol%, relative to the sum of Ni,Mn and Co. In a more preferred embodiment the content is y’ < 20.0 mol%, preferably y’ < 15.0 mol%, and more preferably y’ < 10.0 mol%, relative to the sum of Ni, Mn and Co. In a more preferred embodiment Mn is in a content 0.0 mol% < y’ < 20.0 mol%, preferably 1 .0 mol% < y’ < 15.0 mol%, more preferably 2.0 mol% < y’ < 10.0 mol%, relative to the sum of Ni, Mn and Co.

[0048] A certain preferred embodiment is the positive electrode active material of the invention comprising Li, Ni, Mn, Co and oxygen, wherein Mn is in a content y’ > 0.0 mol%, preferably y’ > 5.0 mol%, more preferably y’ > 10.0 mol%, relative to the sum of Ni, Mn and Co. In a certain preferred embodiment the content is y’ < 30.0 mol%, preferably y’ < 25.0 mol%, and more preferably y’ < 20.0 mol%, relative to the sum of Ni, Mn and Co. In a certain preferred embodiment Mn is in a content 0.0 mol% < y’ < 30.0 mol%, preferably 5.0 mol% < y’ < 25.0 mol%, more preferably 10.0 mol% < y’ < 20.0 mol%, relative to the sum of Ni, Mn and Co.

[0049] A preferred embodiment is the positive electrode active material of the invention comprising Li, Ni, Mn, Co and oxygen, wherein Co is in a content z’, wherein 0.0 < z’ < 30.0 mol%, relative to the sum of Ni, Mn and Co. In a more preferred embodiment Co is in a content z’ > 0.0 mol%, preferably z’ > 1 .0 mol%, more preferably z’ > 2.0 mol%, relative to the sum of Ni, Mn and Co. In a preferred embodiment the content is z’ < 20.0 mol%, preferably z’ < 15.0 mol%, and more preferably z’ < 10.0 mol%, relative to the sum of Ni, Mn and Co. In a preferred embodiment Co is in a content 0.0 mol% < z’ < 20.0 mol%, preferably 1.0 mol% < z’ < 15.0 mol%, more preferably 2.0 mol% < z’ < 10.0 mol%, relative to the sum of Ni, Mn and Co.

[0050] A certain preferred embodiment is the positive electrode active material of the invention comprising Li, Ni, Mn, Co and oxygen, wherein Co is in a content z’ > 0.0 mol%, preferably z’ > 5.0 mol%, more preferably z’ > 10.0 mol%, relative to the sum of Ni, Mn and Co. In a preferred embodiment the content is z’ < 30.0 mol%, preferably z’ < 25.0 mol%, and more preferably z’ < 20.0 mol%, relative to the sum of Ni, Mn and Co. In a preferred embodiment Co is in a content 0.0 mol% < z’ < 30.0 mol%, preferably 5.0 mol% < z’ < 25.0 mol%, more preferably 10.0 mol% < z’ < 20.0 mol%, relative to the sum of Ni, Mn and Co.

[0051] A more preferred embodiment is the positive electrode active material of the invention comprising Li, Ni, Mn, Co and oxygen, wherein:a. Ni in a content x’, wherein 40.0 < x’ < 98.0 mol%, relative to the sum of Ni, Mn, and Co, b. Mn in a content y’, wherein 0.0 < y’ < 30.0 mol%, relative to the sum of Ni, Mn, and Co, c. Co in a content z’, wherein 0.0 < z’ < 30.0 mol%, relative to the sum of Ni, Mn, and Co, wherein x’, y’ and z’ are measured by ICP-OES.

[0052] A more highly preferred embodiment is the positive electrode active material of the invention comprising Li, Ni, Mn, Co and oxygen, wherein: a. Ni in a content x’ between 75.0 mol% < x’ < 92.0 mol%, preferably 78.0 mol% < x’ < 90.0 mol%, more preferably 80.0 mol% < x’ < 88.0 mol%, relative to the sum of Ni, Mn and Co, b. Mn in a content 0.0 mol% < y’ < 20.0 mol%, preferably 1 .0 mol% < y’ < 15.0 mol%, more preferably 2.0 mol% < y’ < 10.0 mol%, relative to the sum of Ni, Mn and Co, c. Co in a content 0.0 mol% < z’ < 20.0 mol%, preferably 1 .0 mol% < z’ < 15.0 mol%, more preferably 2.0 mol% < z’ < 10.0 mol%, relative to the sum of Ni, Mn and Co, and wherein x’, y’ and z’ are measured by ICP-OES.

[0053] As appreciated by the skilled person the amount of Li, Ni, Mn and Co in the positive electrode active material is measured by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Worded differently x’, y’ and z’ are measured by ICP- OES. For example, but not limiting to the invention, an Agilent ICP 720-ES is used in the ICP-OES analysis.

[0054] A preferred embodiment is the positive electrode active material of the invention having a Li / (Ni+Mn+Co) ratio (mol / mol), > 0.90, preferably > 0.92, more preferably > 0.95. A preferred embodiment is the positive electrode active material of the invention having a Li / (Ni+Mn+Co) ratio (mol / mol), < 1.10, preferably < 1.08, more preferably < 1 .05. A preferred embodiment is the positive electrode active material of the invention having a Li / (Ni+Mn+Co) ratio (mol / mol), in the range of 0.90 -1.10, preferably in the range of 0.92 - 1 .08, more preferably in the range of 0.95 - 1 .05.

[0055] A highly preferred embodiment is the positive electrode active material of the invention comprising Li, M’, and oxygen, wherein M’ comprises: a. Ni in a content x, wherein 28.0 < x < 98. 0 mol%, relative to M’, preferably wherein 50.0 < x < 98. 0 mol%, relative to M’, b. Mn in a content y, wherein 0.0 < y < 30.0 mol%, relative to M’, c. Co in a content z, wherein 0.0 < z < 30.0 mol%, relative to M’, d. Si in a content a, wherein 0.0 < a < 5.0 mol%, relative to M’, e. B in a content b, wherein 0.0 < b < 5.0 mol%, relative to M’, f. D in a content d, wherein 0.0 < d < 2.0 mol%, relative to M’, wherein D is an element different from Li, Ni, Mn, Co, Si, B and oxygen; wherein x, y, z, a, b, and d are measured by ICP-OES, and wherein x+y+z+a+b+d is 100.0 mol%.

[0056] A certain preferred embodiment is the positive electrode active material of the invention comprising Li, M’, and oxygen, wherein M’ comprises: a. Ni in a content x, wherein 58.0 < x < 98. 0 mol%, relative to M’, b. Mn in a content y, wherein 0.0 < y < 15.0 mol%, relative to M’, c. Co in a content z, wherein 0.0 < z < 15.0 mol%, relative to M’, d. Si in a content a, wherein 0.0 < a < 5.0 mol%, relative to M’, e. B in a content b, wherein 0.0 < b < 5.0 mol%, relative to M’, f. D in a content d, wherein 0.0 < d < 2.0 mol%, relative to M’, wherein D is an element different from Li, Ni, Mn, Co, Si, B and oxygen; wherein x, y, z, a, b, and d are measured by ICP-OES, and wherein x+y+z+a+b+d is 100.0 mol%.

[0057] As appreciated by the skilled person the amount of Li and M’, preferably Li, Ni, Mn, Co, D and Si, in the positive electrode active material is measured by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Worded differently x, y, z, a, b and d are measured by ICP-OES. For example, but not limiting to the invention, an Agilent ICP 720-ES is used in the ICP-OES analysis.

[0058] A more preferred embodiment is the positive electrode active material of the invention, comprising Li, M’, and oxygen, wherein M’ comprises Ni in a content x > 55.0 mol%, preferably x > 58.0 mol%, more preferably x > 60.0 mol%, relative to M’. In a preferred embodiment Ni is in a content x < 90.0 mol% preferably x < 88 mol%, more preferably x < 85.0 mol%, relative to M’. A more preferred embodiment is the positive electrode active material of the invention, wherein Ni is in a content x between 55.0 mol% < x < 90.0 mol%, preferably 58.0 mol% < x < 88.0 mol%, more preferably 60.0 mol% < x < 85.0 mol%, relative to M’.

[0059] A certain preferred embodiment is the positive electrode active material of the invention comprising Li, M’, and oxygen, wherein M’ comprises Ni in a content x > 55.0 mol%, preferably x > 58.0 mol%, more preferably x > 60.0 mol%, relative to M’. In a certain preferred embodiment Ni is in a content x < 75.0 mol% preferably x < 72 mol%, more preferably x < 70.0 mol%, relative to M’. A more certain preferred embodiment is the positive electrode active material of the invention, wherein Ni is in a content x between 55.0 mol% < x < 75.0 mol%, preferably 58.0 mol% < x < 72.0 mol%, more preferably 60.0 mol% < x < 70.0 mol%, relative to M’.

[0060] A certain preferred embodiment is the positive electrode active material of the invention comprising Li, M’, and oxygen, wherein M’ comprises Ni in a content x > 75.0 mol%, preferably x > 78.0 mol%, more preferably x > 80.0 mol%, relative to M’. In a certain preferred embodiment Ni is in a content x < 92.0 mol% preferably x < 90 mol% and more preferably x < 88.0 mol%, relative to M’. A more certain preferred embodiment is the positive electrode active material of the invention, wherein Ni is in a content x between 75.0 mol% < x < 92.0 mol%, preferably 78.0 mol% < x < 90.0 mol%, more preferably 80.0 mol% < x < 88.0 mol%, relative to M’.

[0061] A more preferred embodiment is the positive electrode active material of the invention, comprising Li, M’, and oxygen, wherein M’ comprises Mn in a content y > 0.0 mol%, preferably y > 1 .0 mol%, more preferably y > 2.0 mol%, relative to M’. In a more preferred embodiment, the content is y < 20.0 mol%, preferably y < 15.0 mol%, more preferably y < 10.0 mol%, relative to M’. In a more preferred embodiment Mn is in a content 0.0 mol% < y < 20.0 mol%, preferably 1 .0 mol% < y < 15.0 mol%, more preferably 2.0 mol% < y < 10.0 mol%, relative to M’.

[0062] A certain preferred embodiment is the positive electrode active material of the invention comprising Li, M’, and oxygen, wherein M’ comprises Mn in a content y > 0.0mol%, preferably y > 5.0 mol%, more preferably y > 10.0 mol%, relative to M’. In a certain preferred embodiment, the content is y < 30.0 mol%, preferably y < 25.0 mol%, more preferably y < 20.0 mol%, relative to M’. In a certain preferred embodiment Mn is in a content 0.0 mol% < y < 30.0 mol%, preferably 5.0 mol% < y < 25.0 mol%, more preferably 10.0 mol% < y < 20.0 mol%, relative to M’.

[0063] A more preferred embodiment is the positive electrode active material of the invention comprising Li, M’, and oxygen, wherein M’ comprises Co in a content z > 0.0 mol%, preferably z > 1 .0 mol%, more preferably z > 2.0 mol%, relative to M’. In a preferred embodiment the content is z < 20.0 mol%, preferably z < 15.0 mol%, and more preferably z < 10.0 mol%, relative to M’. In a preferred embodiment Co is in a content 0.0 mol% < z < 20.0 mol%, preferably 1 .0 mol% < z < 15.0 mol%, more preferably 2.0 mol% < z < 10.0 mol%, relative to M’.

[0064] A certain preferred embodiment is the positive electrode active material of the invention comprising Li, M’, and oxygen, wherein M’ comprises Co in a content z > 0.0 mol%, preferably z > 5.0 mol%, more preferably z > 10.0 mol%, relative to M’. In a preferred embodiment the content is z < 30.0 mol%, preferably z < 25.0 mol%, more preferably z < 20.0 mol%, relative to M’. In a preferred embodiment Co is in a content 0.0 mol% < z < 30.0 mol%, preferably 5.0 mol% < z < 25.0 mol%, more preferably 10.0 mol% < z < 20.0 mol%, relative to M’.

[0065] A preferred embodiment is the positive electrode active material according to the invention comprising Li, M’, and oxygen, wherein M’ comprises Si in a content a > 0.01 mol%, preferably a > 0.03 mol%, more preferably a > 0.06 mol%, relative to M’. In a preferred embodiment the content a < 2.0 mol%, preferably a < 1 .0 mol%, more preferably a < 0.1 mol%, relative to M’. In a preferred embodiment the content a is 0.01 mol% < a< 2.0 mol%, preferably 0.03 mol% < a < 1 .0 mol%, more preferably 0.06 mol% < a < 0.1 mol%, relative to M’.

[0066] A preferred embodiment is the positive electrode active material according to the invention comprising Li, M’, and oxygen, wherein M’ comprises B in a content b > 0.01 mol%, preferably b > 0.1 mol%, more preferably b > 0.4 mol%, relative to M’. In a preferred embodiment the content b < 4.0 mol%, preferably b < 3.0 mol%, more preferably b < 2.0 mol%, relative to M’. In a preferred embodiment the content b is 0.01 mol% < b< 4.0 mol%, preferably 0.1 mol% < b < 3.0 mol%, more preferably 0.4 mol% < b < 2.0 mol%, relative to M’. In certain preferred embodiments the content b is 0.5 mol% < b <4.0 mol%, preferably 0.7 mol% < b < 3.0 mol%, more preferably 0.8 mol% < b < 2.0 mol%, relative to M’.

[0067] As is known to the skilled person, the positive electrode active material of the invention can comprise impurities or be doped or contain metals on the surface resulting in an overall positive electrode active material comprising one or more elements other than Li, Ni, Mn, Co, Si, B and O, which is reflected in the parameter “D” used herein. A preferred embodiment is the positive electrode active material according to the invention comprising D, wherein D is at least one element selected from the group consisting of Al, Ba, Ca, Ce, Cr, Fe, La, Mg, Mo, Nb, S, Sr, Ti, V, W, Y, Zn, and Zr; preferably Al, Ti, Cr, Nb, S, Y, and W; more preferably Al, Ti, Nb, and W.

[0068] A preferred embodiment is the positive electrode active material according to the invention comprising Li, M’, and oxygen, wherein M’ comprises D in a content d > 0.0 mol%, preferably d > 0.25 mol%, more preferably d > 0.5 mol%, relative M’. In a preferred embodiment the content d < 1.75 mol%, preferably d < 1.5 mol%, more preferably d < 1 .25 mol%, relative to M’. In a preferred embodiment the content d is 0.0 mol% < d < 1 .75 mol%, preferably 0.25 mol% < d < 1 .5 mol%, more preferably 0.5 mol% < d < 1 .25 mol%, relative to M’.

[0069] In certain preferred embodiments the positive electrode active material is according to the invention, wherein d = 0.0 mol%, relative to M’.

[0070] A more highly preferred embodiment is the positive electrode active material of the invention comprising Li, M', and oxygen, wherein M' comprises: a. Ni in a content x, wherein 75.0 mol% < x < 92.0 mol%, preferably 78.0 mol%< x < 90.0 mol%, more preferably 80.0 mol% < x < 88.0 mol%, relative to M’, b. Mn in a content y, wherein 0.0 mol% < y < 20.0 mol%, preferably 1 .0 mol%< y < 15.0 mol%, more preferably 2.0 mol% < y < 10.0 mol%, relative to M’, c. Co in a content z, wherein 0.0 mol% < z < 20.0 mol%, preferably 1.0 mol%< z < 15.0 mol%, more preferably 2.0 mol% < z < 10.0 mol%, relative to M’, d. Si in a content a, wherein 0.01 mol% < a < 2.0 mol%, preferably 0.03 mol%< a < 1 .0 mol%, more preferably 0.06 mol% < a < 0.1 mol%, relative to M’, e. B in a content b, wherein 0.01 mol% < b < 4.0 mol%, preferably 0.1 mol% < b < 3.0 mol%, more preferably 0.4 mol% < b < 2.0 mol%, relative to M’,f. D in a content d, wherein 0.0 mol% < d < 1 .75 mol%, preferably 0.25 mol%< d < 1 .5 mol%, more preferably 0.5 mol% < d < 1 .25 mol%, relative to M’, wherein D is an element different from Li, Ni, Mn, Co, Si, B and oxygen; wherein x, y, z, a, b, and d are measured by ICP-OES, and wherein x+y+z+a+b+d is 100.0 mol%.

[0071] A preferred embodiment is the positive electrode active material of the invention having a Li / M’ ratio (mol / mol), preferably a Li / (Ni+Mn+Co) ratio (mol / mol), > 0.90, preferably > 0.92, more preferably > 0.95. A preferred embodiment is the positive electrode active material of the invention having a Li / M’ ratio (mol / mol), preferably aLi / (Ni+Mn+Co) ratio (mol / mol), < 1.10, preferably < 1.08, more preferably < 1.05. A preferred embodiment is the positive electrode active material of the invention having a Li / M’ ratio (mol / mol), preferably a Li / (Ni+Mn+Co) ratio (mol / mol), in the range of 0.90 - 1.10, preferably in the range of 0.92 - 1 .08, more preferably in the range of 0.95 - 1 .05.

[0072] A highly preferred embodiment is the positive electrode active material of the invention according to formula (I):LiW”Nix”Mny”CoZ”Sia”Bb”Dd”O2 (I) a. wherein 0.90 < w” < 1 .10, preferably 0.92 < w” < 1 .08, more preferably 0.95< w” < 1 .05; b. wherein 0.75 < x” < 0.92, preferably 0.78 < x” < 0.90, more preferably 0.80 < x” < 0.88; c. wherein 0.0 < y” < 0.20, preferably 0.01 < y” < 0.15, more preferably 0.02 < y” < 0.10; d. wherein 0.0 < z” < 0.20, preferably 0.01 < z” < 0.15, more preferably 0.02 < z” < 0.10; e. wherein 0.0001 < a” < 0.02, preferably 0.0003 < a” < 0.01 , more preferably 0.0006 < a” < 0.001 ; f. wherein 0.0001 < b” < 0.04, preferably 0.001 < b” < 0.03, more preferably 0.004 < b” < 0.02; g. wherein 0.0001 < d” < 0.0175, preferably 0.0025 < d” < 0.015, more preferably 0.005 < d” < 0.0125; and h. wherein x”+y”+z”+a”+b”+d”=1 .0.

[0073] As appreciated by the skilled person the amounts of w”, x”, y”, z”, a”, b” and d” in the positive electrode active material are measured by 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.

[0074] A preferred embodiment is the positive electrode active material of the invention having a carbon content of more than 100 ppm by total weight of the positive electrode active material, preferably a carbon content more than 150 ppm, more preferably a carbon content more than 200 ppm by total weight of the positive electrode active material. A preferred embodiment is the positive electrode active material of the invention having a carbon content of less than 1000 ppm by total weight of the positive electrode active material, preferably a carbon content less than 750 ppm, more preferably a carbon content less than 550 ppm, by total weight of the positive electrode active material. A preferred embodiment is the positive electrode active material of the invention having a carbon content in the range of 100 ppm and 1000 ppm by total weight of the positive electrode active material, preferably a carbon content in the range of 150 ppm and 750 ppm, more preferably a carbon content in the range of 200 ppm and 550 ppm by total weight of the positive electrode active material.

[0075] As appreciated by the skilled person the carbon content of the positive electrode active material of the invention is measured with a carbon analyzer. For example, but not limiting to the invention, a Horiba Emia-Expert carbon / sulfur analyzer can be used to measure the carbon content. Furthermore, the carbon content of the positive electrode active material of the invention is measured before the exposure test as defined in the present invention.

[0076] In a preferred embodiment of the invention the positive electrode active material of the invention has a carbon uptake of less than 1500 ppm carbon by total weight of the positive electrode active material, preferably a carbon uptake of less than 1300 ppm carbon, more preferably a carbon uptake of less than 1200 ppm carbon by total weight of the positive electrode active material. As appreciated by the skilled person the carbon uptake is measured after the exposure test as defined in the present invention. In a certain preferred embodiment of the invention has a carbon uptake of less than 1000 ppm carbon by total weight of the positive electrode active material, preferably a carbon uptake of less than 500 ppm carbon, more preferably a carbon uptake of less than 445 ppm carbon by total weight of the positive electrode active material.

[0077] In a preferred embodiment of the invention the positive electrode active material of the invention has a carbon uptake of less than 340% carbon by total weight of the positive electrode active material, preferably a carbon uptake of less than 245% carbon, more preferably a carbon uptake of less than 200% carbon by total weight of the positive electrode active material. As appreciated by the skilled person the carbon uptake is measured after the exposure test as defined in the present invention.Surface layer

[0078] The present invention provides the positive electrode active material according to the invention, wherein said positive electrode active material comprises boron in a content BB, wherein BB is expressed as molar fraction of B relative to the total amount of Ni, Mn, Co, and Si and B, as measured by XPS analysis, wherein BB > 0.30.

[0079] In a preferred embodiment the positive electrode active material is according to the invention, wherein BB > 0.35, preferably BB > 0.4, more preferably BB > 0.68. In a preferred embodiment the positive electrode active material is according to the invention, wherein BB < 5.0, preferably BB < 2.0, more preferably BB < 1.0. In a preferred embodiment the positive electrode active material is according to the invention, wherein BB is in the range of 0.35 and 5.0, preferably BB is in the range of 0.4 and 2.0, more preferably BB is in the range of 0.68 and 1 .0.

[0080] In an embodiment the positive electrode active material is according to the invention, wherein said positive electrode active material comprises boron in a content Be, wherein Be is expressed as molar fraction of B relative to the total amount of Ni, Mn and Co, as measured by XPS analysis, wherein Be > 1 .0.

[0081] In a preferred embodiment the positive electrode active material is according to the invention, wherein Be > 3.0 preferably Be > 10.0, more preferably Be > 50.0. In a preferred embodiment Be < 1000.0, preferably Be < 500.0, more preferably Be < 100.0. In a preferred embodiment Be is in the range of 3.0 and 1000.0, preferably Be is in the range of 10.0 and 500.0, more preferably Be is in the range of 50.0 and 100.0.

[0082] In a preferred embodiment the positive electrode active material is according to the invention, wherein the positive electrode active material has a B content BA defined as b / (x+y+z+a+b),a. wherein the positive electrode active material has a B content BB, wherein BB is expressed as molar fraction B relative to the total amount of Ni, Mn, Co, Si, and B, as measured by XPS analysis, and b. wherein the ratio BB / BA > 5.0.

[0083] In a more preferred embodiment the positive electrode active material is according to the invention, wherein the ratio BB / BA > 35, preferably the ratio BB / BA > 45, more preferably ratio BB / BA > 72. In a more preferred embodiment the positive electrode active material is according to the invention, wherein the ratio BB / BA < 1000, preferably the ratio BB / BA < 500, more preferably ratio BB / BA < 100. In a more preferred embodiment the positive electrode active material is according to the invention, wherein the ratio BB / BA is in the range of 35 and 1000, preferably the ratio BB / BA in the range of 45 and 500, more preferably the ratio BB / BA in the range of 72 and 100.

[0084] In the context of the present invention, BB or Be is the molar fraction of B relative to the total amount of Ni, Mn, Co, Si and B or relative to the total amount of Ni, Mn and Co respectively measured in a region of a particle of the positive electrode active material according to invention defined between a first point of an external edge of said particle and a second point at a distance from said first point. Said distance separating said first to said second point being equal to a penetration depth of said XPS, said penetration depth D’ being comprised between 1.0 to 10.0 nm. In particular, the penetration depth is the distance along an axis perpendicular to a virtual line tangent to said external edge and passing trough said first point.

[0085] The external edge of the particle is, in the framework of this invention, the boundary or external limit distinguishing the particle from its external environment. Therefore, XPS analysis provides atomic content of elements in an uppermost layer of a particle with a penetration depth of about 10.0 nm from an outer boundary of the particle. The outer boundary of the particle is also referred to as “surface”. For example, but not limiting to the invention, XPS analysis is carried out with a Thermo K-a+ spectrometer (Thermo Scientific).

[0086] In the framework of the present invention, at% signifies atomic percentage. The at% or “atomic 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. Further in the framework of the present invention the designation at% is equivalent to mol% or “molar percent”.

[0087] As appreciated by the skilled person the defined ratio BB / BA refers to the positive electrode active material of the invention having an enriched amount of B in the surface layer of the positive electrode active material. The surface layer of the positive electrode active material is 1 to 10 nm of the uppermost part of the positive electrode active material. Worded differently, the positive electrode active material of the invention comprises a surface layer of B. For example, but not limiting to the invention, a compound of B present in the surface layer of the positive electrode active material is Li BO2, LiBsOs, LiBsOs or combinations thereof.

[0088] A highly preferred embodiment of the invention is the positive electrode active material according to the invention, wherein said positive electrode active material comprises silicon in a content Sis, wherein Sis is expressed as molar fraction of Si relative to the total amount of Ni, Mn, Co, and Si and B, as measured by XPS analysis, wherein Sis > 0.01 .

[0089] In a preferred embodiment the positive electrode active material is according to the invention, wherein Sis > 0.03, preferably Sis > 0.05, more preferably Sis > 0.08. In a preferred embodiment the positive electrode active material is according to the invention, wherein Sis < 1.0, preferably Sis < 0.3, more preferably Sis < 0.2. In a preferred embodiment the positive electrode active material is according to the invention, wherein Sis is in the range of 0.03 and 1 .0, preferably Sis is in the range of 0.05 and 0.3, more preferably Sis is in the range of 0.08 and 0.2.

[0090] In an embodiment the positive electrode active material is according to the invention, wherein said positive electrode active material further comprises silicon in a content Sic, wherein Sic is expressed as molar fraction Si relative to the total amount of Ni, Mn and Co, as measured by XPS analysis, wherein Sic > 0.3.

[0091] In a preferred embodiment the positive electrode active material is according to the invention, wherein Sic > 0.5, preferably Sic > 1.0, more preferably Sic > 5.0. In a preferred embodiment Sic < 500.0, preferably Sic < 100.0, more preferably Sic < 50.0. In a preferred embodiment Sic is in the range of 0.5, and 500.0, preferably Sic is in the range of 1 .0 and 100.0, more preferably Sic is in the range of 5.0, and 50.0.

[0092] In a preferred embodiment the positive electrode active material is according to the invention, wherein the positive electrode active material has a Si content SiA defined as a / (x+y+z+a+b),a. wherein the positive electrode active material has a Si content Sis, wherein Sis is expressed as molar fraction Si relative to the total amount of Ni, Mn, Co, Si, and B, as measured by XPS analysis, and b. wherein the ratio Sis / SiA > 30.0.

[0093] In a more preferred embodiment the positive electrode active material is according to the invention, wherein the ratio Sis / SiA > 35, preferably the ratio Sis / SiA > 50, more preferably ratio Sis / SiA > 100. In a more preferred embodiment the positive electrode active material is according to the invention, wherein the ratio Sis / SiA < 1000, preferably the ratio Sis / SiA < 400, more preferably ratio Sis / SiA < 250. In a more preferred embodiment, the positive electrode active material is according to the invention, wherein the ratio Sis / SiA is in the range of 35 and 1000, preferably the ratio Sis / SiA in the range of 50 and 400, more preferably the ratio Sis / SiA in the range of 100 and 250.

[0094] In the context of the present invention, Sis or Sic is the molar fraction of Si relative to the total amount of Ni, Mn, Co, Si and B or relative to the total amount of Ni, Mn and Co respectively measured in a region of a particle of the positive electrode active material according to invention defined between a first point of an external edge of said particle and a second point at a distance from said first point. Said distance separating said first to said second point being equal to a penetration depth of said XPS, said penetration depth D’ being comprised between 1.0 to 10.0 nm. In particular, the penetration depth is the distance along an axis perpendicular to a virtual line tangent to said external edge and passing trough said first point.

[0095] As appreciated by the skilled person the defined ratio Sis / SiA refers to the positive electrode active material of the invention having an enriched amount of Si in the surface layer of the positive electrode active material. The surface layer of the positive electrode active material is 1 to 10 nm of the uppermost part of the positive electrode active material. Worded differently, the positive electrode active material of the invention comprises a surface layer of Si. For example, but not limiting to the invention, a compound of Si present in the surface layer of the positive electrode active material is Li2SiOs.In the context of the present invention the positive electrode active material may comprise, besides the enriched amount of boron and silicon, further D, wherein D is at least one element selected from the group consisting of Al, Ba, Ca, Ce, Cr, Fe, La, Mg, Mo,Nb, S, Sr, Ti, V, W, Y, Zn, and Zr; preferably Al, Ti, Cr, Nb, S, Y, and W; more prefera- bly AI, Ti, Nb, and W.

[0096] A certain preferred embodiment concerns the positive electrode active material of the invention having a. a BB content in the range of 0.35 and 5.0, preferably BB in the range of 0.4 and 2.0, more preferably BB in the range of 0.68 and 1 .0; and b. a Sis content in the range of 0.03 and 1 .0, preferably in the range of 0.05 and 0.3, more preferably in the range of 0.08 and 0.2.

[0097] A certain preferred embodiment concerns the positive electrode active material of the invention having a. a ratio BB / BA in the range of 35 and 1000, preferably the ratio BB / BA in the range of 45 and 500, more preferably the ratio BB / BA in the range of 72 and 100; and b. a Sis content in the range of 0.03 and 1 .0, preferably in the range of 0.05 and 0.3, more preferably in the range of 0.08 and 0.2.

[0098] A certain preferred embodiment concerns the positive electrode active material of the invention having a. a ratio BB / BA in the range of 35 and 1000, preferably the ratio BB / BA in the range of 45 and 500, more preferably the ratio BB / BA in the range of 72 and 100; and b. a ratio Sis / SiA in the range of 35 and 1000, preferably the ratio Sis / SiA in the range of 50 and 400, more preferably the ratio Sis / SiA in the range of 100 and 250.Morphology

[0099] In certain preferred embodiments the present invention provides the positive electrode active material according to the invention, wherein said positive electrode active material is a powder comprising single particles and / or secondary particles, wherein each of the single particles consist of only one primary particle and each of the secondary particles consist of at least two primary particles and at most twenty primary particles as observed in a SEM image. Preferably, at least 30% of the particles, more preferably at least 50% of the particles, constituting the powder observed in a SEM image arethe single particles and / or the secondary particles. The number of primary particles constituting the single particles and / or the secondary particles are determined in a field of view of at least 45 pm x at least 60 pm (i.e. of at least 2700 pm2), preferably of: at least 100 pm x 100 pm (i.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.

[0100] 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.

[0101] Certain preferred embodiments concern the positive electrode active material of the invention being said powder comprising the single particles and / or the secondary particles, wherein the particles constituting said powder have a particle median D50 value of less than 15 pm, preferably less than 10 pm, more preferably less than 5 pm. Certain preferred embodiments concern the positive electrode active material of the invention , wherein the particles constituting said powder have a particle median D50 value of more than 1 pm, preferably more than 2 pm, more preferably more than 3 pm. Certain preferred embodiments concern the positive electrode active material of the invention, wherein the particles constituting said powder have a particle median D50 value between 1 and 15 pm, preferably between 2 and 10 pm, more preferably between 3 and 5 pm.

[0102] As appreciated by the skilled person the particle size distribution (PSD) D50 of the positive electrode active material powder is measured by laser diffraction particle size analysis. Preferably, the D50 is defined as a volume median particle size, more preferably the particle size at 50% of the cumulative volume% distributions obtained from the Malvern Mastersizer 3000 with Hydro MV measurements. For example, but not limiting to the invention, the particle median D50 can be measured using a Malvern Mastersizer 3000.

[0103] In certain preferred embodiment, said positive electrode active material of the invention comprises polycrystalline particles.

[0104] As appreciated by the skilled person the polycrystalline particles are agglomerated by more than 20 primary particles, preferably 50 or more primary particles, more preferably 100 or more primary particles. Hence, in certain preferred embodiments said positive electrode active material is a powder comprising polycrystalline particles, wherein each of the polycrystalline particles consist of more than 20 primary particles, preferably 50 or more primary particles, more preferably 100 or more primary particle as observed in a SEM image. Preferably, at least 30% of the particles, more preferably at least 50% of the particles, constituting the powder observed in a SEM image are polycrystalline particles. The number of primary particles constituting the polycrystalline particles are determined in a field of view of at least 45 pm x at least 60 pm (i.e. of at least 2700 pm2), preferably of: at least 100 pm x 100 pm (i.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.

[0105] Formation of the polycrystalline particles occurs after a thermal treatment step.

[0106] In certain highly preferred embodiments said positive electrode active material has a polycrystalline morphology.

[0107] Certain preferred embodiments concern the positive electrode active material of the invention comprising said powder comprising said polycrystalline particles wherein the particles constituting said powder have a particle median D50 value of less than 15 pm, preferably less than 10 pm, more preferably less than 5 pm. Certain preferred embodiments concern the positive electrode active material of the invention, wherein said particle median D50 value of more than 1 pm, preferably more than 2 pm, more preferably more than 3 pm. Certain preferred embodiments concern the positive electrode active material of the invention, wherein said particle median D50 value between 1 and 15 pm, preferably between 2 and 10 pm, more preferably between 3 and 5 pm. Preferably said positive electrode active material has a poly-crystalline morphology.

[0108] Certain embodiments concern the positive electrode active material of the invention a. is said powder comprising the single particles and / or the secondary particles;b. having a Co content Coedge as measured by cross-sectional EDS (CS-EDS) at an edge of the particles, wherein Coedge is expressed as mol% relative to the sum of Ni, Mn, and Co content as measured by CS-EDS at the edge of the particles, wherein the particles have a Co content Cocenter as measured by CS-EDS at a center of the particle, wherein Cocenter is expressed as mol% relative to the sum of Ni, Mn, and Co content as measured by CS- EDS at the center of the particles, and wherein the ratio Coedge I Cocenter > 1.10, preferably Coedge / Cocenter > 1 .20, more preferably Coedge I Cocenter >1 .30, most preferably Coedge I Cocenter >1 .50; and / or c. having an Al content AIA defined as c / (x+y+z+c), wherein c is the content of Al as measured by XPS, and wherein the positive electrode active material has a Al content AIB, wherein AIB is determined by XPS analysis, wherein AIB is expressed as a molar fraction relative to the total amount of Co, Mn, Ni and Al as measured by XPS analysis, wherein the ratio AIB / AIA > 1 .0, preferably the ratio AIB I AIA > 2.0, more preferably the ratio AIB I AIA > 2.5, even more preferably the ratio AIB I AIA > 3.0, even more preferably the ratio AIB I AIA > 3.5, most preferably the ratio AIB I AIA > 4.0.

[0109] Certain embodiments concern the positive electrode active material according to the invention a. is said powder comprising the single particles and / or the secondary particles, and b. having a carbon content in the range of 100 ppm and 400 ppm by total weight of the positive electrode active material, preferably a carbon content in the range of 150 ppm and 350 ppm, more preferably a carbon content in the range of 200 ppm and 300 ppm by total weight of the positive electrode active material.

[0110] Certain preferred embodiments concern the positive electrode active material according to the invention a. is said powder comprising the single particles and / or the secondary particles, and b. having a carbon uptake of less than 900 ppm carbon by total weight of the positive electrode active material, preferably a carbon uptake of less than500 ppm carbon, more preferably a carbon uptake of less than 445 ppm carbon by total weight of the positive electrode active material.

[0111] Certain preferred embodiments concern the positive electrode active material according to the invention a. is said powder comprising the single particles and / or the secondary particles, and b. having a carbon uptake of less than 250% carbon by total weight of the positive electrode active material, preferably a carbon uptake of less than 200% carbon, more preferably a carbon uptake of less than 198% carbon by total weight of the positive electrode active material.

[0112] Certain preferred embodiments concern the positive electrode active material according to the invention a. is said powder comprising the polycrystalline particles, preferably the positive electrode active material having a polycrystalline morphology, and b. having a carbon content in the range of 250 ppm and 1000 ppm by total weight of the positive electrode active material, preferably a carbon content in the range of 300 ppm and 750 ppm, more preferably a carbon content in the range of 400 ppm and 550 ppm by total weight of the positive electrode active material.

[0113] Certain preferred embodiments concern the positive electrode active material according to the invention a. is said powder comprising the polycrystalline particles, preferably the positive electrode active material having a polycrystalline morphology, and b. having a carbon uptake of less than 1600 ppm carbon by total weight of the positive electrode active material, preferably a carbon uptake of less than 1500 ppm carbon, more preferably a carbon uptake of less than 1450 ppm carbon by total weight of the positive electrode active material.

[0114] Certain preferred embodiments concern the positive electrode active material according to the invention a. is a powder comprising said polycrystalline particles, preferably the positive electrode active material having a polycrystalline morphology, andb. having a carbon uptake of less than 340% carbon by total weight of the positive electrode active material, preferably a carbon uptake of less than 245% carbon, more preferably a carbon uptake of less than 200% carbon by total weight of the positive electrode active material.Method

[0115] In a second aspect the invention provides a method for manufacturing a positive electrode active material, wherein said method comprises: step a) mixing a lithium transition metal-based oxide compound with a source of silicon and a source of boron, and step b) heating the mixture at a temperature under 500 °C for a time between 1 hour and 20 hours so as to obtain the positive electrode active material.

[0116] In a highly preferred embodiment of the method for manufacturing a positive electrode active material of the invention the positive electrode active material is according to the first aspect of the invention. As appreciated by the skilled person, in case the method for manufacturing a positive electrode active material of the invention affords the positive electrode material according to the first aspect of the invention, all embodiments directed to the positive electrode active material according to the first aspect of the invention apply mutatis mutandis to the method for manufacturing the positive electrode active material according to the first aspect of the invention. For example, the various embodiments relating to the identity and amounts of Li, M’, BA, BB, SSA, Sis and carbon content as explained herein in the context of the positive electrode active material are equally applicable to the method for the preparation of said positive electrode active material.

[0117] In a preferred embodiment of the method the lithium transition metal-based oxide compound comprises Li, M’” and oxygen, wherein M’” comprises Ni, Mn, Co and D’”, wherein D’” is an element different from Li, Ni, Mn and Co, preferably D’” is at least one element selected from the group consisting of Al, Ba, Ca, Ce, Cr, Fe, La, Mg, Mo, Nb, S, Sr, Ti, V, W, Y, Zn, Si, B and Zr; preferably Al, Ti, Cr, Nb, S, Y, and W; more preferably Al, Ti, Nb, and W. Preferably, the lithium transition metal-based oxide used is typically prepared according to a lithiation process, which is the process wherein a mixture of a transition metal oxide precursor and a further source of lithium is heated at a temperature preferably of at least 500 °C and at most 1000 °C. Typically, the transitionmetal oxide precursor is prepared by coprecipitation of one or more transition metal sources, such as salts, preferably sulfates or nitrates, more preferably sulfates; of the elements Ni, Mn and / or Co, in the presence of an alkali compound, such as an alkali hydroxide e.g. sodium hydroxide and / or ammonia. Preferably, the further source of lithium is metallic lithium or a lithium salt, preferably a lithium salt such as LiOH.

[0118] In a preferred embodiment said lithium transition metal-based oxide compound comprises Li, M’” and oxygen, wherein M’” comprises Ni, Mn, Co and D’”, wherein a. Ni in a content x’”, wherein 75.0 mol% < x’” < 92.0 mol%, preferably 78.0 mol% < x’” < 90.0 mol%, more preferably 80.0 mol% < x’” < 88.0 mol%, relative to M’”, b. Mn in a content y’”, wherein 0.0 mol% < y’” < 20.0 mol%, preferably 1 .0 mol% < y’” < 15.0 mol%, more preferably 2.0 mol% < y’” < 10.0 mol%, relative to M’”, c. Co in a content z’”, wherein 0.0 mol% < z’” < 20.0 mol%, preferably 1 .0 mol% < z’” < 15.0 mol%, more preferably 2.0 mol% < z’” < 10.0 mol%, relative to M’”, d. D’” in a content d’”, wherein 0.0 mol% < d’” < 1 .75 mol%, preferably 0.25 mol% < d’” < 1 .5 mol%, more preferably 0.5 mol% < d’” < 1 .25 mol%, relative to M’”, wherein D’” is an element different from Ni, Mn, Co and oxygen; wherein x’”, y’”, z’” and d’” are measured by ICP-OES, and wherein x’” + y’” + z’” + d’” = 100.0 mol%.

[0119] In a preferred embodiment of the method, the source of silicon is a Si-alkoxide, an alkylalkoxy silane or a polysiloxane, preferably an alkylalkoxy silane or a polysiloxane, more preferably a polysiloxane.

[0120] In a preferred embodiment of the method the source of silicon is a Si-alkoxide, preferably SiOR1R2R3R4, wherein R1, R2, R3and R4are independently selected from H and Ci-Cs alkyl or alkenyl optionally substituted with a halide, preferably C1-C4 alkyl, more preferably C1-C2 alkyl.

[0121] In a more preferred embodiment of the method, the source of silicon is a Si- alkoxide being SiOR54, wherein R5is a Ci-Cs alkyl or alkenyl optionally substituted with a halide, preferably a C1-C4 alkyl, more preferably a C1-C2 alkyl. In a highly preferred the source of Si is silicon tetraethoxide.

[0122] In a highly preferred embodiment of the method the source of silicon is an alkylalkoxy silane, more preferably R6a(R7O)bSi with a = 0 , 1 , 2 or 3; b = 1 , 2 or 3; a + b = 4; and R6and R7independently selected from the group consisting of H and Ci-Cs alkyl or alkenyl optionally substituted with a halide, preferably a C1-C4 alkyl, more preferably a C1-C2 alkyl; more preferably R6and R7are the same alkyl group selected from the group consisting of a Ci-Cs alkyl or alkenyl optionally substituted with a halide, preferably a C1-C4 alkyl, more preferably a C1-C2 alkyl; most preferably the source of silicon is methyltrimethoxy silane.

[0123] In a highly preferred embodiment, the source of silicon is a polysiloxane, preferably a polydialkylsiloxane, wherein the alkyl is selected from Ci-Cs alkyl or alkenyl optionally substituted with a halide, preferably C1-C4 alkyl, more preferably C1-C2 alkyl; more preferably a polydimethylsiloxane. In a highly preferred embodiment, the source of silicon is polysiloxane being a hydroxy terminated polydimethylsiloxane or a trimethylsiloxy terminated polydimethylsiloxane, preferably a hydroxy terminated polydimethylsiloxane. The present invention is not limited to a particular polydimethylsiloxane having a specific number average molecular weight Mn. Such polymers are commercially available in a variety of different number average molecular weights. Preferably, the hydroxy terminated polydimethylsiloxane or the trimethylsiloxy terminated polydimethylsiloxane has a number average molecular weight Mnbetween 200 g / mol and 1 000 000 g / mol, preferably between 300 g / mol and 150 000 g / mol, most preferably between 400 g / mol and 10 000 g / mol, such as about 410 g / mol or 4200 g / mol.

[0124] In a certain preferred embodiment, mixing the lithium transition metal-based oxide compound with the source of silicon, in particular when the source of silicon is a solid, occurs through dry-mixing of said lithium transition metal-based oxide compound with said source of silicon. As appreciated by the skilled person dry-mixing means that no additional solvent is added to the mixture of the lithium transition metal-based oxide compound and the source of silicon.

[0125] In a certain preferred embodiment of the method the source of silicon is added to a first liquid, in particular when the source of silicon is the alkylalkoxy silane as defined in the present invention, preferably the source of silicon is dissolved in the first liquid. Preferably the first liquid is water. Preferably, the lithium transition metal-based oxide compound with the source of silicon added to the first liquid is further mixed with a second liquid, preferably the second liquid comprises water and an alcohol, more preferably the second liquid is a mixture of water and an alcohol. Preferably, the alcohol ismethanol, ethanol, propanol, butanol or a mixture thereof, preferably methanol or ethanol, more preferably ethanol. In a preferred embodiment the weight ratio of alcohol to water (meaning the overall content of water present in the first liquid and the second liquid) is between 10:1 and 1 :10, preferably between 5:1 and 1 :5, more preferably 2:1 and 1 :2.

[0126] In a preferred embodiment the Si content in the source of silicon is at least 0.01 wt.%, relative to the total weight of the lithium transition metal-based oxide compound, preferably at least 0.05 wt.%, more preferably at least 0.08 wt.% relative to the total weight of the lithium transition metal-based oxide compound. In a preferred embodiment the Si content in the source of silicon is at most 1 .0 wt.%, relative to the total weight of the lithium transition metal-based oxide compound, preferably at most 0.5 wt.%, more preferably at most 0.22 wt.% relative to the total weight of the lithium transition metalbased oxide compound. In a preferred embodiment the Si content in the source of silicon is in the range of 0.01 and 1 .0 wt.%, relative to the total weight of the lithium transition metal-based oxide compound, preferably in the range of 0.05 and 0.5 wt.%, more preferably in the range of 0.08 and 0.22 wt.% relative to the total weight of the lithium transition metal-based oxide compound.

[0127] In a preferred embodiment mixing said lithium transition metal-based oxide compound with a source of boron is dry-mixing of said lithium transition metal-based oxide compound with a source of boron, in particular when said source of boron is a solid. As appreciated by the skilled person dry-mixing means that no additional solvent is added to the mixture of the lithium transition metal-based oxide compound and the source of boron.

[0128] In a preferred embodiment the source of boron is boric acid (H3BO3), boron oxide (B2O3) or a borate salt such as sodium tetrahydroxyborate (NaB(OH)4), trisodium orthoborate (NasBOs), sodium perborate (Na2H4B20s), sodium meta borate (NasBsOe) and the like, preferably the source of boron is boric acid (H3BO3).

[0129] In a preferred embodiment the B content in the source of boron is at least 0.01 wt.%, relative to the total weight of the lithium transition metal-based oxide compound, preferably at least 0.02 wt.%, more preferably at least 0.04 wt.% relative to the total weight of the lithium transition metal-based oxide compound. In a preferred embodiment the B content in the source of boron is at most 1 .0 wt.%, relative to the total weight of the lithium transition metal-based oxide compound, preferably at most 0.5 wt.%, morepreferably at most 0.22 wt.% relative to the total weight of the lithium transition metalbased oxide compound. In a preferred embodiment the B content in the source of boron is in the range of 0.01 and 1 .0 wt.%, relative to the total weight of the lithium transition metal-based oxide compound, preferably in the range of 0.02 and 0.5 wt.%, more preferably in the range of 0.04 and 0.22 wt.% relative to the total weight of the lithium transition metal-based oxide compound.

[0130] In a preferred embodiment of the method the heating of the mixture is at a temperature of more than 275 °C, preferably more than 300 °C, most preferably more than 325 °C. In a preferred embodiment of the method the heating of the mixture is a temperature of less than 450 °C, preferably less than 400 °C, more preferably less than 375 °C. In a preferred embodiment of the method the heating of the mixture is at a temperature between a. 275 °C and 450 °C, preferably between 300°C and 400 °C, more preferably between 325°C and 375 °C.

[0131] In a preferred embodiment of the method is the heating of the mixture of at least2 hours, preferably at least 3 hours, more preferably at least 5 hours. In a preferred embodiment of the method is the heating of the mixture of at most 15 hours, preferably at most 10 hours, more preferably at most 7 hours. In a preferred embodiment of the method is the heating of the mixture between 2 hours and 15 hours, preferably between3 hours and 10 hours, more preferably between 5 hours and 7 hours.

[0132] In a more preferred embodiment of the method is the heating of the mixture a. at a temperature between 275 °C and 450 °C, preferably between 300°C and 400 °C, more preferably between 325 and 375 °C; and b. between 2 hours and 15 hours, preferably between 3 hours and 10 hours, more preferably between 5 hours and 7 hours.

[0133] A preferred embodiment of the method is the heating of the mixture under an oxidizing atmosphere. Preferably, the oxidizing atmosphere comprises oxygen, such as air, or consists of oxygen.

[0134] In a more preferred embodiment, the heating of the mixture occurs under an oxidizing atmosphere in a furnace.Product-by-process

[0135] In another aspect the invention concerns the positive electrode active material obtainable by the method according to the second aspect of the invention. As appreciated by the skilled person all embodiments directed to the positive electrode active material according to the first aspect of the invention and / or the method according to the second aspect of the invention apply mutatis mutandis to the positive electrode active obtainable by the method according to the invention. For example, the various embodiments relating to the identity and amounts of Li, M’, SIA, Sis, BB, BA, the source of silicon and the source of boron as explained herein in the context of the positive electrode active material or the method for manufacturing said positive electrode active material are equally applicable to the positive electrode active material obtainable by the method for the preparation of the positive electrode active material.Battery

[0136] In another aspect the invention concerns a battery comprising the positive electrode active material according to the first aspect of the invention and / or the positive electrode active material obtainable by the method according to the third aspect of the invention.

[0137] In a preferred embodiment the battery is a solid-state battery. Preferably the solid-state battery comprises a sulfide-based electrolyte. Preferably said electrolyte is a sulfide based solid electrolyte, more preferably the electrolyte comprises Li, P, and S. Typically, the following sulfur containing compounds of LiePSsX with X being F, Br, Cl or I, preferably Br or CI; thio-LISICON (Li3.25Ge0.25P0.75S4), Li2S-P2Ss-LiCI, Li2S-SiS2, Lil- Li2S-SiS2, Li2S-P2S5-LiCI, Li2S-SiS2, Lil-Li2S-SiS2, Lil-Li2S-P2S5, Lil-Li2S-P2O5, Lil- Li3PO4-P2S5, Li2S-P2Ss, Li3PS4, Li PsSn, Lil-Li2S-B2S3, Li3PO4-Li2S-SiS2, Li3PO4-Li2S- SiS2, Li3PO4-Li2S-SiS2, LiioGeP2Si2, Li9.54Si1.74P1.44S11.7d03, and / or LiyPsSn may be suitably used. In a highly preferred embodiment the battery is a sulfide solid-state battery.

[0138] Preferably, the solid-state battery further comprises an anode comprising anode active material. Suitable electrochemically active anode materials are those known in the art. For example, the anode may comprise graphitic carbon, metallic lithium or a metal alloy comprising lithium, such as Li-ln alloy, as the anode active material.

[0139] In a preferred embodiment the battery according to the invention, preferably the solid-state battery comprising the sulfide-based electrolyte as defined herein, has anefficiency of at least 88%, preferably at least 89%, more preferably at least 90%, even more preferably at least 91 %, even more preferably at least 91.3%, even more preferably at least 92%, most preferably at least 94%. As appreciated by the skilled person the efficiency of the battery is determined, wherein the initial charge capacity (CQ1 ) and discharge capacity (DQ1 ) are measured in constant current mode (CC) at C rate of 0.1 C in voltage range from 4.3 V to 2.5 V (Li / Li+) or from 3.7 V to 1 .9 V (ln-Li / Li+). The efficiency (%) of the reversible capacity is obtained according to an equation below: DQEfficiency (%) = — X 100(%) C 1

[0140] Preferably, the schedule uses a 1 C current definition of 160 mA / g.

[0141] In a preferred embodiment the battery according to the invention has first discharge capacity of at least 200.0 mAh / g, more preferably of at least 205.0 mAh / g, even more preferably of at least 209.0 mAh / g, even more preferably of at least 210.0 mAh / g, most preferably of at least 212 mAh / g. As understood by the skilled person the first discharge capacity (DQ1 ) is measured in constant current mode (CC) at C rate of 0.1 C in voltage range: 4.3 V to 2.5 V (Li / Li+) or 3.7 V to 1 .9 V (lnLi / Li+).Use

[0142] In another aspect the present invention concerns a use of the positive electrode active material according to the first aspect of the invention and / or the positive electrode active material obtainable by the method according to the third aspect of the invention in a battery.

[0143] A preferred embodiment is the use of the positive electrode active material in a battery, preferably a solid-state-battery, more preferably a sulfide solid-state-battery, to increase the efficiency of the battery and / or to increase the first discharge capacity of said battery.

[0144] In another aspect the present invention concerns a use of the battery according to the fourth aspect of the invention in either one of a portable computer, a tablet, a mobile phone, an energy storage system, an electric vehicle or in a hybrid electric vehicle, preferably in an electric vehicle or in a hybrid electric vehicle.EXAMPLES

[0145] The following analysis methods are used in the Examples:

[0146] Inductively coupled plasma - optical emission analysis (ICP-OES) : The contents of the elements in positive electrode active material examples and comparative example as described herein below are measured by the Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) method using an Agilent ICP 720-OES. 1 gram of a powder sample 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, B, and Si are expressed as at.% of the total of these contents.

[0147] Particle size: The PSD is measured using a Malvern Mastersizer 3000 with Hydro MV wet dispersion accessory after dispersing examples as described herein below of positive electrode active material powders in an aqueous medium. To improve the dispersion of the positive electrode 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.Sulfide solid-state rechargeable cell testSulfide solid-state rechargeable cell preparation

[0148] Positive electrode preparation: For the preparation of a positive electrode, a slurry contains positive electrode active material powder, Li-P-S based solid electrolyte, carbon (Super-P, Timcal), and binder (RC-10, Arkema) - with a formulation of 64.0 : 30.0 : 3.0 : 3.0 by weight - in butyl acetate solvent is mixed in Ar-filled glove box. The slurry is casted on one side of an aluminum foil followed by drying the slurry coated foil in a vacuum oven to obtain a positive electrode. The obtained positive electrode is punched with a diameter of 10 nm wherein the active material loading amount is around 4 mg / cm2

[0149] Negative electrode preparation: For the preparation of a negative electrode, Li foil (diameter 3 mm, thickness 100 pm) is placed centered on the top of In foil (diameter 10 nm, thickness 100 pm) and pressed to form Li-ln alloy negative electrode.

[0150] Separator preparation: For the preparation of a separator which also has a function of the solid electrolyte in a battery, the Li-P-S based solid electrolyte is pelletized with a pressure of 250 MPa to obtain 100 pm pellet thickness.

[0151] Cell assembling: A sulfide solid-state rechargeable battery is assembled in an Ar- fi lied glovebox with such order from bottom to top: positive electrode comprising Al current collector with the coated part on the top - separator - negative electrode with Li side on the top - Cu current collector. The stacked components are pressed together with a pressure of 250 MPa and placed in an external cage to prevent air exposure.

[0152] Testing method : The testing method is a conventional “constant cut-off voltage” test. Each cell is cycled at 60 °C using a Toscat-3100 computer-controlled galvanostatic cycling station (from Toyo).

[0153] The schedule uses a 1 C current definition of 160 mA / g. The initial charge capacity (CQ1 ) and discharge capacity (DQ1 ) are measured in constant current mode (CC) at C rate of 0.1 C in voltage range from 4.3 V to 2.5 V (Li / Li+) or from 3.7 V to 1 .9 V (In- Li / Li+). The efficiency (%) of the irreversible capacity is obtained according to an equation below: 100(%).

[0154] Exposure test: The carbon exposure test is conducted by evenly spreading 40 grams of positive electrode active material on a 95 x 95 mm2dish and place the dish inside a 30 °C chamber. The atmosphere of the chamber is controlled so as to have a relative humidity level of 50%. After 3 days (72 hours), the positive electrode active material powder is taken for the carbon analysis as described in method E. Increase of carbon content is calculated according to the equation below wherein Cbefore is the content of carbon before exposure and Carter is the content of carbon after exposure:

[0155] Carbon analysis: The content of carbon of the positive electrode active material powder is measured by Horiba Emia-Expert carbon / sulfur analyzer. 1 gram of the positive electrode active material powder is placed in a ceramic crucible in a high frequency induction furnace. 1 .5 grams of tungsten and 0.2 grams of tin are added into the crucible as accelerators. The powder is heated at a programmable temperature whereingases produced during the combustion are then analyzed by Infrared detectors. The analysis of CO2 and CO determines the carbon concentration.

[0156] X-ray Photoelectron Spectroscopy (XPS): 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, i.e., surface layer. Therefore, all elements measured by XPS are contained in the surface layer.

[0157] 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 pm and measurement angle of 45 °. A wide survey scan to identify elements present at the surface is conducted at 200 eV pass energy. C1 s 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.

[0158] 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 1 a. Line shape GL(30) is the Gaussian / Lorentzian product formula with 70% Gaussian line and 30% Lorentzian line.

[0159] Table 1 a. XPS fitting parameter for Ni2p3, Mn2p3, Co2p3, B1 s, and Si 1 p.

[0160] For Ni and Co peak, constraints are set for each defined peak according to Table 1 b.

[0161] Table 1 b. XPS fitting constraints for Ni and Co peak fitting.

[0162] The B and Si surface contents as determined by XPS are expressed as atomic fractions of B and Si, respectively, in the surface layer of the particles divided by the total content of Ni, Mn, Co, B, and Si in said surface layer. It is calculated as follows:

[0163] The present invention is further illustrated in the following examples:

[0164] Comparative Example CEX1 .1 : A polycrystalline positive electrode active material was prepared according to the following steps:Step 1 ) Transition metal oxidized hydroxide precursor preparation: A nickel- based transition metal oxidized hydroxide powder (TMH1 ) having a metal composition Nio.85Mno.07Coo.08 was prepared by a co-precipitation process in a large-scale continuous stirred tank reactor (CSTR) with mixed nickel manganese cobalt sulfates, sodium hydroxide, and ammonia.Step 2) Mixing: the TMH1 prepared from Step 1 ) was mixed with LiOH in an industrial blender to obtain a first mixture having a lithium to metal (Ni, Mn, and Co) molar ratio of 0.98.Step 3) Heating: The first mixture from Step 2) was heated at 785 °C for 10 hours in an oxidizing atmosphere to obtain CEX1.1 comprising Ni, Mn, and Co in a molar ratio Ni: Mn: Co of 0.85: 0.07: 0.08 as obtained by ICP-OES. CEX1 .1 has a D50 of 4 pm.

[0165] SEM image of CEX1 .1 is shown in Figure 2.

[0166] Comparative Example CEX1.2 was prepared by mixing 100 grams CEX1.1 with 0.43 gram SiCh powder and 0.57 gram H3BO3 powder in an industrial blender followed by heating at 350 °C for 6 hours under a flow of oxygen gas.

[0167] Comparative Example CEX1.3 was prepared by mixing 400 grams CEX1.1 with 2.12 grams of polydimethylsiloxane hydroxy terminated (PDMS-O) in an industrial blender followed by heating at 350 °C for 6 hours under a flow of oxygen gas. PDMS-0 is a liquid with molecular weight of around 4200 g / mol.

[0168] Comparative Example CEX1 .4 was prepared by mixing 400 grams CEX1 .1 with 2.29 grams of H3BO3 in an industrial blender followed by heating at 350 °C for 6 hours under a flow of oxygen gas.

[0169] Examples EX1.1 , EX1.2, EX1.3, EX1.4, EX2 are according to the present invention.

[0170] EX1.1 was prepared by mixing 400 grams CEX1.1 with 2.12 grams of PDMS-0 and 1.14 grams of H3BO3 in an industrial blender followed by heating at 350 °C for 6 hours under a flow of oxygen gas.

[0171] EX1.2 was prepared according to the same method as EX1.1 except that the amount of H3BO3 added was 2.29 grams.

[0172] EX1.3 was prepared according to the same method as EX1.1 except that the amount of HsBOsadded was 4.57 grams.

[0173] EX1 .4 was prepared according to the same method as EX1 .2 except that the amount of PDMS-0 added was 1 .06 grams.

[0174] Comparative Example CEX2.1 : A positive electrode active material powder containing single particles and secondary particles was prepared according to the following steps:Step 1 ) Transition metal oxidized hydroxide precursor preparation: A nickel- based transition metal oxidized hydroxide powder (TMH2) having a metalcomposition Nio.85Mno.07Coo.08 was prepared by a co-precipitation process in a large-scale continuous stirred tank reactor (CSTR) with mixed nickel manganese cobalt sulfates, sodium hydroxide, and ammonia.Step 2) Precursor oxidation: the TMH1 prepared from Step 1 ) was heated at 400 °C for 7 hours in an oxidizing atmosphere to obtain a heated product.Step 3) First mixing: the heated product prepared from Step 2) was mixed with LiOH in an industrial blender to obtain a first mixture having a lithium to metal (Ni, Mn, and Co) molar ratio of 0.96.Step 4) First heating: The first mixture from Step 3) was heated at 890 °C for 11 hours in an oxidizing atmosphere to obtain a first heated product.Step 5) Wet bead milling: The first heated product from Step 4) was bead milled in a solution containing 0.5 mol% Co with respect to the total molar contents of Ni, Mn, and Co in the first heated product followed by drying and sieving process to obtain a milled product. The bead milling solid to solution weight ratio was 6:4 and was conducted for 20 minutes.Step 6) Second mixing: the milled product obtained from Step 5) was mixed in an industrial blender with 1.5 mol% Co from CO3O4 and 7.5 mol% Li from LiOH, each with respect to the total molar contents of Ni, Mn, and Co in the milled product to obtain a second mixture.Step 7) Second heating: The second mixture from Step 6) was heated at 760 °C for 10 hours in an oxidizing atmosphere followed by crushing and sieving with 250 ppm of alumina powder with respect to the weight of the second mixture, to obtain a second heated powder.Step 8) Third mixing: 400 grams of the second heated powder obtained from step 7) was mixed with 2.12 grams PDMS-0 in an industrial blender to obtain a third mixture.Step 9) Third heating: the third mixture obtain from step 8) was heated at 350 °C for 6 hours under a flow of oxygen gas followed by grinding and sieving.

[0175] Comparative Example CEX2.1 comprising Ni, Mn, and Co in a molar ratio Ni: Mn: Co of 0.84: 0.07: 0.09 as obtained by ICP-OES. CEX2.1 has a D50 of 4 pm.

[0176] Due to the wet milling in step 5) CEX2.1 is a powder containing single particles and secondary particles. The SEM image of CEX2.1 is shown in Figure 3.

[0177] Comparative Example CEX2.2 was prepared according to the same method as CEX2.1 except that 2.29 grams of H3BO3 was added in the step 8) instead of PDMS-O.

[0178] EX2 was prepared according to the same method as CEX2.1 except that 2.29 grams of H3BO3 was added in the step 8) together with PDMS-O.Results

[0179] Table 2a. Summary of the process and properties of examples and comparative examples.

[0180] Table 2b Summary of the process and properties of examples and comparative examples - continued

[0181] Table 3. Summary of XPS quantification for examples and comparative examplesn.a. = not available

[0182] Tables 2a and 2b and Table 3 summarize the preparation process and properties of the examples and the comparative examples with main variation in the morphology,Si source, B amount, and Si amount. In the XPS analysis, BB or Sis value higher than 0 indicates that B or Si present on the surface of the positive electrode active material as associated with the XPS measurement which signal is acquired from the first few nanometers (e.g. 1 nm to 10 nm) of the uppermost part of a sample, i.e. surface layer. Onthe other hand, BA or SiA from ICP-OES measurement is the B or Si content of the entire particle. Therefore, the ratio of XPS result to ICP-OES result such as BB / BA or Sis / SiA higher than 1 indicates that said B or Si is present mostly on the surface of the positive electrode active material. The higher BB / BA or Sis / SiA value corresponds with the more B or Si presence on the surface of positive electrode active material.

[0183] CEX1 .3 is a positive electrode active material comprising around 2000 ppm Si from PDMS-0 and CEX1.4 comprises 1000 ppm B. When comparing both materials with EX1.2, which is a positive electrode active material comprising around 2000 ppm Si from PDMS-0 and 1000 ppm B, the EX1.2 exhibit improved electrochemical properties, indicated by higher DQ1 and EF values. The same improvement is observed for EX2 when compared with CEX2.1 and CEX2.2 regardless of the morphology.

[0184] However, when the Si source is SiO2, as represented by CEX1.2, the improvement is not observed although the positive electrode active material comprising the same amount of Si and B. The better performance of EX1 .2 is likely originated from the higher Sis / SiA ratio value. The benefit of positive electrode active material comprising both B and Si is further confirmed by the variation of Si and B amount in EX1 .1 , EX1 .3, and EX1 .4. Furthermore, table 3 shows by the shift of the Si binding energy peak that in CEX1 .2, the chemical state and surrounding environment of Si is different from examples prepared with PDMS-O.

[0185] Moreover, a lower carbon level after 3 days exposure test is also observed for the positive electrode active material comprising both Si and B.

Claims

CLAIMS

1. A positive electrode active material for batteries comprising lithium, oxygen, nickel, and at least one metal selected from the group consisting of manganese and cobalt, comprising a. Ni in a content x’, wherein 40.0 < x’ < 98.0 mol%, relative to the sum of Ni, Mn, and Co, b. Mn in a content y’, wherein 0.0 < y’ < 30.0 mol%, relative to the sum of Ni, Mn, and Co, c. Co in a content z’, wherein 0.0 < z’ < 30.0 mol%, relative to the sum of Ni, Mn, and Co, wherein x’, y’ and z’ are measured by ICP-OES, and wherein said positive electrode active material further comprises boron with a content BB, wherein BB is expressed as molar fraction of B relative to the total amount of Ni, Mn, Co, Si, and B as measured by XPS analysis, wherein BB > 0.30, wherein said positive electrode active material further comprises silicon, wherein said positive electrode active material displaying a peak in binding energy level between 101.4 eV and 106.0 eV, as measured by XPS analysis.

2. The positive electrode active material according to claim 1 , wherein said positive electrode active material displaying a peak in binding energy level between 101.4 eV and 105.0 eV, preferably between 101.5 eV and 104.5 eV, more preferably between 101 .6 eV and 104.0 eV, as measured by XPS analysis.

3. The positive electrode active material according to claim 1 or 2, having a content Sis, wherein Sis is expressed as molar fraction Si relative to the total amount of Ni, Mn, Co, Si, and B as measured by XPS analysis, and wherein Sis > 0.01 .

4. The positive electrode active material according to claim 3, wherein Sis is in the range of 0.03 and 1 .0, preferably Sis is in the range of 0.05 and 0.3, more preferably Sis is in the range of 0.08 and 0.2.

5. The positive electrode active material according to any one preceding claim, wherein BB is in the range of 0.35 and 5.0, preferably BB is in the range of 0.4 and 2.0, more preferably BB is in the range of 0.68 and 1 .0.

6. The positive electrode active material according to any one preceding claim, comprising Li, M’, and oxygen, wherein M’ comprises: a. Ni in a content x, wherein 50.0 < x < 98. 0 mol%, relative to M’, b. Mn in a content y, wherein 0.0 < y < 30.0 mol%, relative to M’, c. Co in a content z, wherein 0.0 < z < 30.0 mol%, relative to M’, d. Si in a content a, wherein 0.0 < a < 5.0 mol%, relative to M’, e. B in a content b, wherein 0.0 < b < 5.0 mol%, relative to M’, f. D in a content d, wherein 0.0 < d < 2.0 mol%, relative to M’, wherein D is an element different from Li, Ni, Mn, Co, Si, B and oxygen, wherein x, y, z, a, b, and d are measured by ICP-OES, and wherein x+y+z+a+b+d is 100.0 mol%.

7. The positive electrode active material according to any one preceding claim, wherein the positive electrode active material has a Si content SiA defined as a / (x+y+z+a+b), wherein the ratio Sis I SiA > 30.0.

8. The positive electrode active material according to any one preceding claim, wherein the positive electrode active material has a B content BA defined as b / (x+y+z+a+b), wherein the ratio BB / BA > 30.0.

9. The positive electrode active material according to any one of claims 6 to 8, comprising a. Ni in a content x, wherein 75.0 mol% < x < 92.0 mol%, preferably 78.0 mol% < x < 90.0 mol%, more preferably 80.0 mol% < x < 88.0 mol%, relative to M’, b. Mn in a content y, wherein 0.0 mol% < y < 20.0 mol%, preferably 1 .0 mol% < y < 15.0 mol%, more preferably 2.0 mol% < y < 10.0 mol%, relative to M’,c. Co in a content z, wherein 0.0 mol% < z < 20.0 mol%, preferably 1.0 mol%< z < 15.0 mol%, more preferably 2.0 mol% < z < 10.0 mol%, relative to M’, d. Si in a content a, wherein 0.01 mol% < a < 2.0 mol%, preferably 0.03 mol% < a < 1 .0 mol%, more preferably 0.06 mol% < a < 0.1 mol%, relative to M’, e. B in a content b, wherein 0.01 mol% < b < 4.0 mol%, preferably 0.1 mol%< b < 3.0 mol%, more preferably 0.4 mol% < b < 2.0 mol%, relative to M’, f. D in a content d, wherein 0.0 mol% < d < 1 .75 mol%, preferably 0.25 mol% < d < 1 .5 mol%, more preferably 0.5 mol% < d < 1 .25 mol%, relative to M’.

10. The positive electrode active material according to any preceding claim, wherein the positive electrode active material is a powder single particles and / or secondary particles, wherein each of the single particles consist of only one primary particle and each of the secondary particles consist of at least two primary particles and at most twenty primary particles as observed in a SEM image.

11. The positive electrode active material according to claim 10, wherein at least 30% of the particles, more preferably at least 50% of the particles, constituting the powder observed in a SEM image are the single particles and / or the secondary particles.

12. The positive electrode active material according to any one of claims 1 to 10, wherein the positive electrode active material is a powder comprising polycrystalline particles, wherein each of the polycrystalline particles consist of more than 20 primary particles as observed in a SEM image.

13. The positive electrode active material according to any one preceding claim having a carbon uptake of less than 340% carbon by total weight of the positive electrode active material, preferably a carbon uptake of less than 245% carbon, more preferably a carbon uptake of less than 200% carbon by total weight of the positive electrode active material, wherein the carbon uptake is measured by an exposure test.

14. A method for manufacturing a positive electrode active material, preferably the positive electrode active material according to any one of claims 1 to13, wherein said method comprises: step a) mixing a lithium transition metal-based oxide compound with a source of silicon and a source of boron, and step b) heating the mixture at a temperature under 500 °C for a time between 1 hour and 20 hours so as to obtain the positive electrode active material. wherein the source of Si is a Si-alkoxide, an alkylalkoxy silane or a polysiloxane, preferably a polysiloxane, more preferably a hydroxy-terminated polysiloxane.

15. Method according to claim 14, wherein the source of boron is boric acid (H3BO3), boron oxide (B2O3), sodium tetrahydroxyborate (NaB(OH)4), trisodium orthoborate (NasBOs), sodium perborate (Na2H4B20s), sodium meta borate (NasBsOe) or combinations thereof, preferably the source of boron is boric acid (H3BO3).

16. A solid-state battery comprising the positive electrode active material according to any one of claims 1 to 13.

17. Solid-state battery according to claim 16, comprising a sulfide- based solid electrolyte.

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