Doped positive electrode active material

Abstract

The present invention relates to a positive electrode active material and method for making the same, wherein the positive electrode active material comprises particles comprising Li, M, and O, wherein M consists of Ni in a content x, wherein 50 at% ≤ x < 100 at%, relative to M; Mn in a content y, wherein 0 at% < y ≤ 20 at%, relative to M; Co in a content z, wherein 0 at% < z ≤ 35 at%, relative to M; Nb in a content c, wherein 0 at% < c ≤ 5 at%, relative to M; wherein x, y, z, and c are measured by ICP-OES and x+y+z+c +c=100%; wherein CoXPS / (NiXPS + MnXPS + CoXPS) < z / (x+y+z) and wherein NbXPS > c; NiXPS, MnXPS, CoXPS, NbXPS respectively being the contents of Ni, Mn, Co, Nb relative to M, as measured by XPS; the material further comprising B in a content b, wherein 0 at% ≤ b ≤ 5 at%, S in a content e, wherein 0.0 at% ≤ e ≤ 1.0 at%, relative to M, and D in a content d, wherein 0 at% ≤ d ≤ 2 at%, relative to M, wherein D is at least one element other than Li, Ni, Mn, Co, B, S, and Nb and wherein b, d, and e are measured by ICP-OES.

Description

DescriptionTitleDOPED POSITIVE ELECTRODE ACTIVE MATERIALTechnical Field

[0001] The present disclosure concerns a doped positive electrode active material, in particular for solid state batteries and a method for making the same. The present disclosure further concerns solid state batteries comprising a doped positive electrode active material.Description of Related Art

[0002] Solid-sate rechargeable batteries are of particular interest as they may reach particularly high energy density, combined with a higher level of safety because of the absence of flammable organic liquid electrolyte.

[0003] In rechargeable batteries using liquid electrolytes, typically organic solutions with lithium salts, transition metal dissolution and the formation of unstable cathode-electrolyte interphases may occur, in particular as they tend to decompose, especially at high voltages, producing reactive species like HF that attack cathode surfaces. In contrast, solid electrolytes — such as for example sulfides or oxides — are generally more chemically stable and eliminate metal dissolution, but they suffer from different interfacial reactions that may create resistive layers and mechanical issues like cracking due to volume changes. While interface engineering is critical for both technologies, the problems to be addressed are fundamentally different.

[0004] Various ways for improving the performance of solid-state rechargeable batteries are being explored. Particular aspects such as discharge capacity still need to be improved, preferably improving the efficiency at the same time.Summary

[0005] The present disclosure concerns a positive electrode active material, wherein the positive electrode active material comprises particles comprising Li, M, and O, wherein M consists of: a. Ni in a content x, wherein 50 at% < x < 100 at%, relative to M;b. Mn in a content y, wherein 0 at% < y < 35 at%, relative to M;c. Co in a content z, wherein 0 at% < z < 30 at%, relative to M;d. D in a content d, wherein 0.00 at% < d < 5.0 at%, relative to M, wherein D is at least one element other than Li, Ni, Mn, Co, B, S, and Nbe. Nb in a content c, wherein 0.00 at% < c < 5.0 at%, relative to M;wherein x, y, z, b, c, and d are measured by ICP-OES and x+y+z+b+c+d =100%, wherein Mnxps / (Nixps + Mnxps + COXPS + Nbxps) y / (x+y+z+c) andwherein Nbxps > c, Nixps, Mnxps, COXPS, and Nbxps respectively being the contents of Ni, Mn, Co, and Nb relative to M, as measured by X-ray photoelectron spectroscopy XPS, the particles further comprising S in a content e measured by ICP-OES, wherein 0.0 at% < e < 1.5 at%, relative to M and B in a content b, wherein 0 at% < b < 5 at%, relative to M;.

[0006] The inventors have surprisingly found, that when used in an all solid-state secondary battery, the doped positive electrode active material, surface enriched in Nb and having lower Mn to Ni+Mn+Co ratio at the surface than overall, according to any embodiment or combination of embodiments herein, leads to an increased first cycle discharge capacity (DQ1) as well as an increased efficiency.

[0007] The present disclosure further concerns a method for preparing a positive electrode active material, preferably the positive electrode active material according to any embodiment or combination of embodiments of the present disclosure, comprising:a. mixing a transition metal composite precursor, a Li source, a Co-containing compound, and a Nb-containing compound to obtain a first mixture;b. heating the first mixture at a temperature between 600 °C and 1000 °C to obtain a first heated material;c. optionally mixing the first heated material with a B-containing compound to obtain a second mixture;d. heating the second mixture at a temperature between 250 °C and 500 °C so as to obtain the positive electrode active material.Brief description of figures

[0008] Figure 1 shows examples of STEM-EDS mapping images of Nb and S and a HAADF image showing the EDS measured area.Detailed description

[0009] In the following detailed description, preferred embodiments are described in detail to enable practice of the present disclosure. Although the present disclosure is described with reference to these specific preferred embodiments, it will be understood that the present disclosure is not limited to these preferred embodiments. To the contrary, the present disclosure includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description. Unless otherwise indicated, it is not meant thatthe alternatives, modifications, and equivalents described herein are understood as separate, non-combinable, embodiments. That is, provided it is technically feasible, the different parts of the present disclosure may be combined with one another.

[0010] “at%” signifies atomic percentage. The at% or “atomic percent” of a given element means a percentage of atoms of said element among all atoms in a claimed composition.

[0011] "About" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1 % or less of and from the specified value, in so far such variations are appropriate to perform in the present disclosure. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

[0012] “D50” as used herein refers to a particle size at 50% of cumulative volume% distribution when measured by laser scattering method. The method of measuring D50 by laser scattering method is described herein below.

[0013] As used herein, a range of values “from X to Y” and “between X and Y” include the endpoints of X and Y.

[0014] “Milling” as used herein is the action of reducing the size of particles by a mechanical action submitting the particles to a stress. Some cracks will appear under the stress, and subsequently the particle will be broken in different parts.

[0015] Here within, elemental contents x, y, z, b, c, d, and e are always atomic percentages relative to M.

[0016] In an embodiment, the positive electrode active material of the present disclosure comprises secondary particles consisting of a plurality of primary particles. The secondary particles may in particular consist of more than 20 primary particles. The number of primary particles constituting a secondary particle may be determined by counting the primary particles observed in a Scanning Electron Microscope (SEM) image at a magnification of 2000 from a top view, where the whole shape of the particle is taken. In the context of the present disclosure, primary particles may be 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.

[0017] In an embodiment the positive electrode active material of the present disclosure, 7 < SB / SG, wherein SB is the atomic contents of S relative to total amount of Ni, Mn, and Co on a surface of a primary particle, and SG is the atomic contents of S relative to total amount of Ni, Mn,and Co inside a primary particle, measured by cross-sectional Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive X-ray Spectroscopy (EDS) measurement STEM-EDS.

[0018] In an embodiment of the positive electrode active material of the present disclosure, 200 < Bxps / b, wherein BXPS is atomic content of B relative to total amount of M measured by XPS. Advantageously, 100 < Bxps / b, 50 < Bxps / b. Furthermore, Bxps / b may be such that Bxps / b < 4000, Bxps / b < 2000, Bxps / b < 1000 or even Bxps / b < 500.

[0019] In an embodiment of the positive electrode active material of the present disclosure, 1 < Nba / Nbc, preferably 3 < Nba / Nbc, and more preferably 5 < Nba / Nbc, wherein Nbs is the atomic contents of Nb relative to total amount of Ni, Mn, and Co on a surface of a primary particle, and Nbc is the atomic contents of Nb relative to total amount of Ni, Mn, and Co inside a primary particle, measured by cross-sectional TEM-EDS.

[0020] In an embodiment of the positive electrode active material of the present disclosure, 8 < SB / SG, preferably 9 < SB / SG, and more preferably 10 < SB / SG.

[0021] In an embodiment of the positive electrode active material of the present disclosure, 55 at% < x < 98 at%, preferably 58 at% < x < 96 at%, more preferably 60 at% < x < 95 at%, even more preferably 70 at% < x < 95 at% relative to M.

[0022] In an embodiment of the positive electrode active material of the present disclosure, 1 at% < y < 18 at%, preferably 2 at% < y < 15 at%, and more preferably 3 at% < y < 13 at%, relative to M.

[0023] In an embodiment of the positive electrode active material of the present disclosure, 1 at% < z < 18 at%, preferably 2 at% < z < 15 at%, and more preferably 3 at% < z < 13 at%, relative to M.

[0024] In an embodiment of the positive electrode active material of the present disclosure, b is at least 0.1 at%, advantageously at least 0.2 at%, at least 0.3 at%, or even at least 0.4 at%.

[0025] In an embodiment of the positive electrode active material of the present disclosure, b is at most 4.0 at%, advantageously at most 3.5 at% or less, at most 3.0 at%, at most 2.5 at%, at most 2.0 at%, at most 1.5 at%, or even at most 1.2 at%.

[0026] In an embodiment of the positive electrode active material of the present disclosure, c is at least 0.05 at%, advantageously at least 0.10 at%, at least 0.15 at%, or even at least 0.20 at%.

[0027] In an embodiment of the positive electrode active material of the present disclosure, c is at most 4.0 at%, advantageously at most 3.5 at%, at most 3.0 at%, at most 2.5 at%, at most 2.0 at%, at most 1.5 at%, at most 1.0 at%, or even at most 0.5 at%.

[0028] In an embodiment of the positive electrode active material of the present disclosure, D is at least one element selected from Al, Zr, W, Sr, Sb, Ti, Ba, Ca, Cr, F, Fe, Mg, Mo, Y, V, and Zn. Advantageously D is at least one element selected from the group consisting of Al, Sr, Zr, and W.

[0029] In an embodiment of the positive electrode active material of the present disclosure, d is at least 0.05 at%, advantageously at least 0.10 at%, at least 0.15 at%, or even at least 0.20 at%.

[0030] In an embodiment of the positive electrode active material of the present disclosure, d is at most 4.0 at%, advantageously at most 3.5 at% or less, at most 3.0 at%, or even at most 2.5 at%.

[0031] In an embodiment of the positive electrode active material of the present disclosure, e is at least 0.1 at%, advantageously at least 0.2 at%, at least 0.3 at%, or even at least 0.4 at%.

[0032] In an embodiment of the positive electrode active material of the present disclosure, e is at most 1.4 at%, advantageously at most 1.3 at% or less, at most 1.2 at%, at most 1.1 at%, at most 1.0 at%, at most 0.9 at%, or even at most 0.8 at%.

[0033] In an embodiment of the positive electrode active material of the present disclosure, Coxps / (Nixps + Mnxps + COXPS + Nbxps)>z / (x+y+z+c).

[0034] In an embodiment of the positive electrode active material of the present disclosure, Mnxps / (Nixps + Mnxps + COXPS + Nbxps) < y / (x+y+z+c).

[0035] In an embodiment of the positive electrode active material of the present disclosure, the Li / M molar ratio ranges from 0.9 to 1.1. This range of lithium content may ensure sufficient lithium for electrochemical cycling while avoiding excess lithium that could lead to unwanted side reactions.

[0036] In an embodiment of the positive electrode active material of the present disclosure, the O / M molar ratio ranges from 1.9 to 2.2. This range of oxygen content may ensure proper crystal structure formation while avoiding oxygen deficiencies or excesses that could impact performance.

[0037] In an embodiment of the present disclosure the positive electrode active material is according to formula (I)Lii-NixMnyCOzDdBbNbcSeOo (I), wherein 0.9 < L < 1.2 and 1.9 and 1.9 < o < 2.2.

[0038] In an embodiment of the method of the present disclosure, the Nb-containing compound in step a. is at least one selected from niobium acid, niobium oxide, niobium hydroxide, niobium ethoxide, niobium oxalate, and lithium niobium oxide.

[0039] In an embodiment of the method of the present disclosure, the Co-containing compound in step a. is at least one selected from cobaltic acid, cobalt oxide, cobalt hydroxide, cobalt sulfate, and lithium cobalt oxide.

[0040] In an embodiment of the method of the present disclosure, wherein the B-containing compound in step a. is at least one selected from boric acid, boron oxide, and lithium boron oxide.

[0041] In an embodiment of the method of the present disclosure, the transition metal composite precursor comprises a hydroxide or oxyhydroxide of Nickel, Manganese and Cobalt.

[0042] In an embodiment of the method of the present disclosure, the transition metal composite precursor comprises M’, wherein M’ consists of:a. Ni in a content x’, wherein 50 at% < x’ < 100 at%, relative to M’;b. Mn in a content y’, wherein 0 at% < y’ < 35 at%, relative to M’;c. Co in a content z’, wherein 0 at% < z’ < 30 at%, relative to M’;d. D’ in a content d’, wherein 0.00 at% < d’ < 5.0 at%, relative to M’, wherein d’ is at least one element other than Li, Ni, Co, Mn, and S,wherein x’, y’, z’, and d’ are measured by ICP-OES and x’+y’+z’+d’ =100%the transition metal composite precursor further comprising S in a content e’, measured by ICP-OES , wherein 0.0 at% < e’ < 1.5 at%, relative to M’.

[0043] In an embodiment of the positive electrode active material of the present disclosure, 55 at% < x’ < 98 at%, preferably 58 at% < x’ < 96 at%, more preferably 60 at% < x’ < 95 at%, and even more preferably 70 at% < x’ < 95 relative to M’.

[0044] In an embodiment of the positive electrode active material of the present disclosure, 1 at% < y’ < 18 at%, preferably 2 at% < y’ < 15 at%, and more preferably 3 at% < y’ < 13 at%, relative to m.

[0045] In an embodiment of the positive electrode active material of the present disclosure, 1 at% < z’ < 18 at%, preferably 2 at% < z’ < 15 at%, and more preferably 3 at% < z’ < 13 at%, relative to M’.

[0046] In an embodiment of the positive electrode active material of the present disclosure, D’ is at least one element selected from Al, Zr, W, Sr, Sb, Ti, Ba, Ca, Cr, F, Fe, Mg, Mo, Y, V, and Zn. Advantageously D’ is at least one element selected from the group consisting of Al, Sr, Zr, and W.

[0047] In an embodiment of the positive electrode active material of the present disclosure, d’ is at least 0.05 at%, advantageously at least 0.10 at%, at least 0.15 at%, or even at least 0.20 at%, relative to M’.

[0048] In an embodiment of the positive electrode active material of the present disclosure, d’ is at most 4.0 at%, advantageously at most 3.5 at% or less, at most 3.0 at%, or even at most 2.5 at%, relative to M’.

[0049] In an embodiment of the positive electrode active material of the present disclosure, e’ is at least 0.1 at%, advantageously at least 0.2 at%, at least 0.3 at%, or even at least 0.4 at%, relative to M’.

[0050] In an embodiment of the positive electrode active material of the present disclosure, e’ is at most 1.4 at%, advantageously at most 1.3 at% or less, at most 1.2 at%, at most 1.1 at%, at most 1.0 at%, at most 0.9 at%, or even at most 0.8 at%.

[0051] In an embodiment of the method of the present disclosure, the Li source is selected from LiOH, Lithium ethoxide, lithium acetate, lithium sulfate, lithium chloride and lithium carbonate.

[0052] In an embodiment of the method of the present disclosure, the molar ratio of Li to the total amount of Ni, Mn and Co in the first mixture ranges from 0.9 to 1.1.

[0053] The present disclosure further concerns a battery comprising the positive electrode active material according to any embodiment or combination of embodiments of the present disclosure.

[0054] The battery of the present disclosure may in particular be a solid state secondary battery, in particular a lithium solid state secondary battery.

[0055] A lithium secondary battery generally includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode include an active material capable of intercalation and deintercalation of lithium ions.

[0056] The battery of the present disclosure may comprise a solid electrolyte selected from a sulfide solid electrolyte and an oxide solid electrolyte. Example solid electrolytes comprise Lii0GeP2Si2 (LGPS), Argyrodite- type electrolytes, in particular Li6PS5CI (L-P-S), LLZO (Lithium Lanthanum Zirconium Oxide): Li6.4La3Zri.4Tao.6Oi2; LLTO (Lithium Lanthanum Titanium Oxide): Li3xLa2 / 3-xTiO3; NASICON-type: LAGP (Lii.5Alo.5Gei.5(P04)3), LATP (Lii^Alo^Tii^PO^s)-

[0057] The present disclosure further concerns the use of the battery of the present disclosure comprising a cathode active material in an electrically powered device or system selected from the group consisting of: a portable computer, a tablet, a mobile phone, a telecommunication device, a power tool, mobile machinery, a robotic device, an energy storage system, an uninterruptible power supply system, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an extended-range electric vehicle, a fuel cell electric vehicle, a two-wheeler transportation system, a rail vehicle, a marine vessel, an aircraft, an aerospace system.

[0058] The use of the battery of the present disclosure comprising a cathode active material in the above-listed electrically powered devices and systems enables efficient and reliable energydelivery across a wide range of operational environments. The integration of such batteries into consumer electronics (e.g., portable computers, tablets, mobile phones, telecommunication devices) provides compact and lightweight energy sources that support high energy density and long operational life, thereby enhancing user experience and device portability.

[0059] In industrial applications such as power tools, mobile machinery, and robotic devices, the battery enables high discharge rates and robust performance under variable load conditions, contributing to improved productivity and operational flexibility. The use in energy infrastructure systems, including energy storage systems and uninterruptible power supply (UPS) systems, ensures stable and scalable energy management, supporting grid resilience and backup power reliability.

[0060] In transportation systems, the battery supports electrification of mobility platforms, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), extended-range electric vehicles (EREVs), and fuel cell electric vehicles (FCEVs). These applications benefit from the battery’s ability to deliver consistent power output, fast charging capability, and thermal stability, which are critical for safety and performance in both passenger and freight transport. The inclusion of two-wheeler transportation systems, rail vehicles, marine vessels, aircraft, and aerospace systems demonstrates the versatility of the battery across diverse propulsion architectures and regulatory environments.EXPERIMENTAL ANALYSIS USED IN THE EXAMPLES AND THE COMPARATIVE EXAMPLE

[0061] The following analysis methods are used in the Examples and the Comparative Example.A) Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) measurement

[0062] The amount of Ni, Mn, Co, B, S, D and Nb in the positive electrode active material powder is measured with the ICP-OES method by using an Agilent ICP 720-ES (Agilent Technologies). 2 grams of powder sample is dissolved into 10 mL of high purity hydrochloric acid (at least 37 wt% of HCI with respect to the total weight of solution) in an Erlenmeyer flask. The flask is covered by a glass and heated on a hot plate at 380 °C until complete dissolution of the precursor. After being cooled to room temperature, the solution of the Erlenmeyer flask is poured into a 250 mL volumetric flask. Afterwards, the volumetric flask is filled with deionized water up to the 250 mL mark, followed by complete homogenization.B) Particle size analysis

[0063] The particle size distribution (PSD) of the positive electrode active material powder is measured by laser diffraction particle size analysis using a Malvern Mastersizer 3000 with a Aero S unit. A quantity of solid powder is introduced into a venturi with flowing compressed air (~3 atm) to break up agglomerates and introduce a well dispersed sample stream into the detection unit. D50 is defined as the particle size at 50% of the cumulative volume% distributions.C) X-ray Photoelectron Spectroscopy (XPS)

[0064] In the present disclosure, 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. Therefore, all elements measured by XPS are contained in the surface layer.

[0065] For the surface analysis of positive electrode active material powder particles, XPS measurement is carried out using a Thermo K-a+ spectrometer. Monochromatic Al Ka radiation (hu=1486.6 eV) is used with a spot size of 400 mm and measurement angle of 45 °. A wide survey scan to identify elements present at the surface is conducted at 200 eV pass energy. C1s 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.

[0066] 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 1a. Line shape GL(30) is the Gaussian / Lorentzian product formula with 70% Gaussian line and 30% Lorentzian line. Line shape LA(a,p,m) is an asymmetric line-shape, wherein a and p define the spread of the tail on either side of the Lorentzian component and wherein m specifies the width of the Gaussian used to convolute the Lorentzian curve. Full width at half maximum (FWHM) are useful indicators of chemical state changes and physical influences. That is, broadening of a peak may indicate: a change in the number of chemical bonds contributing to a peak shape, a change in the sample condition (x-ray damage) and / or differential charging of the surface (localized differences in the charge state of the surface)

[0067] Table 1a. XPS fitting parameter for Ni2p, Mn2p, Co2p, B1s, and Nb5d.

[0068] For Ni peaks, constraints are set for each defined peak according to Table 1b.

[0069] Table 1b. XPS fitting constraints for Ni peak fitting.

[0070] COXPS, the surface contents of Co as determined by XPS is expressed as atomic fractions of Co in the surface layer of the particles divided by the total contents of Ni, Mn, Co, and Nb in said surface layer. The surface contents of Co is calculated as following:D) Sulfide solid-state rechargeable cell test - SSBD1) Sulfide solid-state rechargeable cell preparationD1.1) Positive electrode preparation

[0071] 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 cast on one side of an aluminum foil followed and the slurry coated foil is dried in a vacuum oven to obtain a positive electrode foil. The obtained positiveelectrode foil is punched with a diameter of 10 mm to obtain a positive electrode wherein the active material loading amount is around 4 mg / cm2.D1.2) Negative electrode preparation

[0072] For the preparation of a negative electrode, Li foil (diameter 3 mm, thickness 100 pm) is placed centered on the top of an In foil (diameter 9 mm, thickness 100 pm) and pressed to form Li-ln alloy negative electrode.D1.3) Separator preparation

[0073] 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.D1.4) Cell assembling

[0074] A sulfide solid-state rechargeable battery is assembled in an Ar-filled glovebox in the following order from the bottom to the 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.D2) Testing method

[0075] 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).

[0076] The schedule uses a 1C 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 (ln-Li / Li+). The efficiency (%) of the irreversible capacity is obtained according to an equation below:100(%).E) Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive X-ray Spectroscopy (EDS) measurement

[0077] The electron microscopic images were measured by Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive X-ray Spectroscopy (EDS) after making a lamella from a particle by using Focus Ion Beam (FIB) so as to obtain a cross-sectional image. The sample was coated with C before preparing the FIB lamella, then the FIB lamella was prepared on a Cu Omniprobe TEM grid using a Thermo Fisher Helios FIB-SEM. The final thinning of the sample was done using 2kV. Before the TEM measurement, the sample was plasma cleaned 3 times in an argon plasma for 10 seconds at a power of 30 %. The High Angle Annular Dark FieldScanning Transmission Electron Microscopy (HAADF-STEM) and EDS were performed on an aberration corrected FEI Titan TEM at 300 kV, using a Super X detector.

[0078] The atomic contents of Nbs and SB relative to total amount of Ni, Mn, and Co on a surface of a primary particle were determined by measuring elemental concentrations within an area starting at the primary particle surface and extending inwards up to 5% of the primary particle’s cross-sectional circular equivalent diameter.

[0079] The atomic contents of Nbc and SG relative to total amount of Ni, Mn, and Co inside a primary particle were determined by measuring elemental concentrations within an area starting at a distance of 10 % of the primary particle’s cross-sectional circular equivalent diameter from the particle’s surface and extending inwards. The cross-sectional circular equivalent diameter of a primary particle, usually having an irregular shape, is the diameter of a two-dimensional disk having an equivalent area to the cross-section of the primary particle as determined by an image analysis method. The electron microscopic images may be processed with an image analysis software such as for example Imaged (developed by the National Institutes of Health, USA) to identify the primary particles. In Figure 1 shows the distribution of Nb and S is presented by STEM-EDS mapping in Fig. 1 (I) and (II). Nbc and SG were analyzed from area A and Nbs and SB were analyzed from area B shown using HAADF in Fig. 1 (III).EXAMPLES

[0080] The present invention is further illustrated in the following examples.Comparative Example 1 (CEX1)

[0081] A positive electrode active material CEX1 was obtained through following steps:a. Co-precipitation: a transition metal-based oxidized hydroxide precursor with metal composition of Ni0.86Mn0.07Co0.07 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.b. First mixing: the precursor prepared in step a. was mixed homogeneously with LiOH to prepare a first mixture, wherein the molar ratio of Li to total amount of Ni, Mn, and Co is 1.02.c. First heating: the first mixture was heated at 750 °C for 10 hours under oxygen atmosphere followed by cooling, grinding, and sieving to prepare a first heated material.d. Second mixing: the first heated material was mixed homogeneously with H3BO3 powder to prepare a second mixture, wherein 1000 ppm B relative to the weight of the first heated material was added.e. Second heating: the second mixture was heated at 300 °C for 6 hours followed by cooling, grinding, and sieving so as to obtain CEX1.Comparative Example 2 (CEX2)

[0082] A positive electrode active material CEX2 was obtained through the same method as the preparing method of CEX1, except that CO3O4 was mixed with LiOH in step b., wherein 2.5 at% Co relative to total amount of Ni, Mn, and Co in the transition metal precursor was added.Comparative Example 3 (CEX3)

[0083] A positive electrode active material CEX3 was obtained through the same method as the preparing method of CEX1, except that Nb20s was mixed with LiOH in step b., wherein 0.3 at% Nb relative to total amount of Ni, Mn, and Co was added.Example 1 (EX1)

[0084] A positive electrode active material EX1 was obtained through the same method as the preparing method of CEX1, except that CO3O4 and Nb20s were mixed with LiOH in step b., wherein 2.5 at% Co and 0.3 at% Nb relative to total amount of Ni, Mn, and Co in the transition metal precursor were added.

[0085] Table 2 summarizes elemental compositions analyzed by ICP-OES and by TEM-EDS and electrochemical properties such as DQ1 and Efficiency.

[0086] Table 2. Summary of elemental compositions and electrochemical properties for CEX1, CEX2, CEX3, and EX1>>

[0087] Table 3 - Summary of STEM-EDS measurements

[0088] Table 4 - composition and solid state battery (SSB) results

[0089] As can be seen from table 4, EX1 surprisingly shows in addition to the surface enrichment in Nb a lower Mn to Ni+Mn+Co ratio at the surface (XPS data) than overall (ICP data). EX1 also shows an increased first cycle discharge capacity (DQ1) as well as an increased efficiency. The STEM-EDS Data also shows the surface enrichment in Nb as well as in S.

[0090] Furthermore EX1 has a Cobalt distribution such that Coxps / (Nixps + Mnxps + COXPS) > z / (x+y+z), but the difference is less than for the comparative examples

[0091] It was also observed in this material that comprises secondary particles comprising a plurality of primary particles, that in the invention examples the amounts of NbBand SB found at the surface of the primary particles was larger than the amount of NbGand SG respectively found inside the primary particles.

[0092] As can be seen from table 4 above, an all solid-state secondary battery using the positive electrode active material according to invention example EX1 leads to an increased first cycle discharge capacity (DQ1) as well as an increased efficiency.

Claims

Claims

1. A positive electrode active material, wherein the positive electrode active material comprises particles comprising Li, M, and O, wherein M consists of:a. Ni in a content x, wherein 50 at% < x < 100 at%, relative to M;b. Mn in a content y, wherein 0 at% < y < 35 at%, relative to M;c. Co in a content z, wherein 0 at% < z < 30 at%, relative to M;d. B in a content b, wherein 0 at% < b < 5 at%, relative to M;e. S in a content e, wherein 0.0 at% < e < 1.5 at%, relative to M;f. D in a content d, wherein 0.00 at% < d < 5.0 at%, relative to M, wherein D is at least one element other than Li, Ni, Mn, Co, B, S, and Nbg. Nb in a content c, wherein 0.00 at% < c < 5.0 at%, relative to M;wherein x, y, z, b, c, d and e are measured by ICP-OES and x+y+z+b+c+d+e =100%, wherein Mnxps / (Nixps + Mnxps + COXPS + Nbxps) <y / (x+y+z+c) and wherein Nbxps > c, Nixps, Mnxps, COXPS, and Nbxps respectively being the contents of Ni, Mn, Co, and Nb relative to M, as measured by X-ray photoelectron spectroscopy XPS.

2. Positive electrode active material according to claim 1 comprising secondary particles consisting of a plurality of primary particles.

3. Positive electrode active material according to claim 2 having SB / SG S 7, wherein SB is the atomic contents of S relative to total amount of Ni, Mn, and Co on a surface of a primary particle, and SG is the atomic contents of S relative to total amount of Ni, Mn, and Co inside a primary particle, measured by cross-sectional Scanning Transmission Electron Microscopy and Energy Dispersive X-ray Spectroscopy measurement STEM- EDS.

4. Positive electrode active material according to claim 2 or claim 3 having 1 < Nba / Nbc, wherein Nbs is the atomic contents of Nb relative to total amount of Ni, Mn, and Co on a surface of a primary particle, and Nbc is the atomic contents of Nb relative to total amount of Ni, Mn, and Co inside a primary particle, measured by cross-sectional TEM-EDS.

5. Positive electrode active material according to any one preceding claim having 200 < Bxps / b, wherein BXPS is atomic content of B relative to total amount of M measured by XPS.

6. Positive electrode active material according to any one preceding claim wherein c is at least 0.05 at% and / or at most 4.0 at%.

7. Positive electrode active material according to any one preceding claim wherein D is at least one element selected from Al, Zr, W, Sr, Sb, Ti, Ba, Ca, Cr, F, Fe, Mg, Mo, Y, V, and Zn.

8. Positive electrode active material according to any one preceding claim wherein d is at least 0.05 at% and or at most 4.0 at%.

9. Positive electrode active material according to any one preceding claim wherein e is at least 0.1 at%.

10. A method for preparing a positive electrode active material, preferably the positive electrode active material according to any of preceding claims, comprising: a. mixing a transition metal composite precursor, a Li source, a Co-containing compound, and a Nb-containing compound to obtain a first mixture; b. heating the first mixture at a temperature between 600 °C and 1000 °C to obtain a first heated material;c. mixing the first heated material with a B-containing compound to obtain a second mixture;d. heating the second mixture at a temperature between 250 °C and 500 °C so as to obtain the positive electrode active material.

11. Method for preparing a positive electrode active material according to claim 10, wherein the Nb-containing compound in step a. is at least one selected from niobium acid, niobium oxide, niobium hydroxide, niobium ethoxide, niobium oxalate, and lithium niobium oxide.

12. Method for preparing a positive electrode active material according to claim 10 or 11 , wherein the Co-containing compound in step a. is at least one selected from cobaltic acid, cobalt oxide, cobalt hydroxide, cobalt sulfate, and lithium cobalt nitrate.

13. Method for preparing a positive electrode active material according to any of claims 10 to 12, wherein the B-containing compound in step a. is at least one selected from boric acid, boron oxide, and lithium boron oxide.

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

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

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