Lithium nickel-based complex oxides as positive electrode active materials for rechargeable lithium-ion batteries

Abstract

A positive electrode active material for a solid-state battery, the positive electrode active material comprising Li, M' and oxygen, wherein M' comprises: - Ni in a content x between 50.0 mol% and 75.0 mol%; - Co in a content y between 0.0 mol% and 40.0 mol%; - Mn in a content z between 0.0 mol% and 40.0 mol%; - a dopant in a content a between 0.0 mol% and 2.0 mol%; - Zr in a content b between 0.1 mol% and 5.0 mol%, wherein x + y + z + a + b is 100.0 mol%, wherein the Zr content ZrB of the positive electrode active material is expressed as a molar fraction compared to the sum of the molar fractions of Co, Mn, Ni and Zr as measured by XPS analysis, wherein ZrB / ZrA > 50.0, the positive electrode active material comprising secondary particles having a plurality of primary particles, the primary particles having an average diameter between 170 nm and 340 nm.

Description

[0001] Technical Field and Background Technology

[0002] This invention relates to lithium nickel-based oxide positive electrode active materials for solid-state batteries suitable for electric vehicle (EV) and hybrid electric vehicle (HEV) applications, wherein the positive electrode active material comprises lithium nickel-based oxide particles containing zirconium (Zr).

[0003] Positive electrode active materials are defined as materials that are electrochemically active in a positive electrode. For active materials, it is essential to understand their ability to capture and release lithium ions when subjected to voltage changes over a predetermined time period.

[0004] In the framework of this invention, at% represents atomic percentage. At% or “atomic percentage” in a given elemental expression of concentration means what percentage of all atoms in the claimed compound are atoms of the element. Specifying “at%” is equivalent to the term “mol%” or “molar percentage”.

[0005] The weight percentage (wt%) of the first element E in the material (E) wt1 The first element E in the material can be determined by applying the following formula: given atomic percentage (at%) (E) at1 Conversion: Where E at1 and aw1 (E aw1 It is the product of the atomic weight (or molecular weight) of the first element E and the atomic weights (or molecular weights) of the other elements in the material. at1 ×E aw1 The sum, where n is an integer representing the number of different elements contained in the material.

[0006] The purpose of this invention is to provide a positive electrode active material for a solid-state battery having an improved initial charge capacity of at least 160 mAh / g. Summary of the Invention

[0007] This objective is achieved by providing a positive electrode active material for solid-state batteries, wherein the positive electrode active material comprises Li, M', and oxygen, wherein M' comprises:

[0008] -Ni, the content of which x is between 50.0 mol% and 75.0 mol% relative to M';

[0009] -Co, the content of which is y relative to M' is between 0.0 mol% and 40.0 mol%;

[0010] -Mn, the content of which z is between 0.0 mol% and 40.0 mol% relative to M',

[0011] - D, the content a of which is between 0.0 mol% and 2.0 mol% with respect to the total atomic content of M’, wherein D comprises at least one element of Al, B, Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, W and Zn, and

[0012] - Zr, the content b of which is between 0.1 mol% and 5.0 mol% with respect to M’,

[0013] - wherein x, y, z, a and b are measured by ICP,

[0014] - wherein x + y + z + a + b is 100.0 mol%,

[0015] wherein the positive electrode active material has a Zr content Zr defined as A wherein the positive electrode active material has a Zr content Zr B wherein Zr B is determined by XPS analysis, wherein Zr B is expressed as a molar fraction compared to the sum of the molar fractions of Co, Mn, Ni and Zr measured by XPS analysis,

[0016] wherein the ratio Zr B / Zr A > 50.0,

[0017] wherein the positive electrode active material comprises secondary particles having a plurality of primary particles,

[0018] wherein the primary particles have an average diameter between 170 nm and 340 nm, the average diameter being determined by the method of the invention.

[0019] The present invention relates to the following embodiments:

[0020] Embodiment 1

[0021] In a first aspect, the present invention relates to a positive electrode active material for a solid-state battery, wherein the positive electrode active material comprises Li, M’ and oxygen, wherein M’ comprises:

[0022] - Ni, the content x of which is between 50.0 mol% and 75.0 mol% with respect to M’;

[0023] - Co, the content y of which is between 0.0 mol% and 40.0 mol% with respect to M’;

[0024] - Mn, the content z of which is between 0.0 and 70.0 mol% with respect to M', preferably Mn, the content z of which is between 0.0 and 40.0 mol% with respect to M',

[0025] - D, the content a of which is between 0.0 and 2.0 mol% with respect to the total atomic content of M', wherein D comprises at least one element among Al, B, Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, W and Zn, and

[0026] - Zr, the content b of which is between 0.1 and 5.0 mol% with respect to M',

[0027] - wherein x, y, z, a and b are measured by ICP,

[0028] - wherein x + y + z + a + b is 100.0 mol%,

[0029] wherein the positive electrode active material has a Zr content Zr defined as Zr A wherein the positive electrode active material has a Zr content Zr B wherein Zr B is determined by XPS analysis, wherein Zr B is expressed in mole fraction in percentage compared to the sum of the mole fractions of Co, Mn, Ni and Zr measured by XPS analysis, wherein the ratio Zr B / Zr A > 50.0,

[0030] Note that Zr A is the Zr content of the positive electrode active material determined by ICP and is expressed in percentage with respect to the sum of the contents of Co, Ni, Mn and Zr.

[0031] Preferably, Zr B / Zr A is at least 80, preferably at least 100, more preferably at least 130. Preferably, Zr B / Zr A is at most 500, more preferably at most 300, and most preferably at most 200.

[0032] Preferably, the positive electrode active material comprises secondary particles having a plurality of primary particles, and wherein said primary particles have an average diameter between 170 nm and 340 nm, preferably between 200 nm and 340 nm, said average diameter being determined by measuring the primary particle size in images taken by SEM.

[0033] More preferably, the primary particles have an average diameter of at least 180 nm, preferably 200 nm, preferably 220 nm, even more preferably at least 225 nm.

[0034] Preferably, the primary particles have an average diameter of at most 330 nm, preferably at most 320 nm, more preferably at most 300 nm, even more preferably at most 250 nm.

[0035] Preferably, the primary particles have an average diameter of between 180 nm and 330 nm, preferably between 200 nm and 320 nm, more preferably between 220 nm and 310 nm, even more preferably between 225 nm and 250 nm.

[0036] As understood by the person skilled in the art, the primary particle size is determined by measuring the particle size of the primary particles in images taken by SEM.

[0037] Preferably, x > 55.0 mol% and more preferably x > 60.0 mol%

[0038] Preferably, y > 0 mol% and more preferably y > 5.0 mol% and even more preferably y > 10.0 mol%

[0039] In another embodiment, the content of Ni x is between 55 mol% and 72 mol% with respect to M' and the content of Co y is between 0.0 mol% and 20.0 mol% with respect to M'.

[0040] In a preferred embodiment, the content of Ni x is > 55.0 mol%, preferably x > 60.0 mol%, more preferably x > 62.0 mol%. In a preferred embodiment, x < 72.0 mol%, preferably x < 70.0 mol%, and more preferably x < 68.0 mol%.

[0041] In a more preferred embodiment, the content of Ni x is between 55.0 mol% < x < 72.0 mol%, preferably 60.0 mol% < x < 70.0 mol%, more preferably 62.0 mol% < x < 68.0 mol%.

[0042] As understood by the person skilled in the art, the amount of Li and M' in the positive electrode active material, preferably the amount of Li, Ni, Mn, Co, D and Zr, is measured with Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). For example, but not limited to the present application, Agilent ICP 720-ES is used in the ICP-OES analysis.

[0043] In preferred embodiments, the content z of Mn is > 0.0 mol%, more preferably z > 5.0 mol%, and even more preferably z > 8.0 mol%. In preferred embodiments, the content is z < 40.0 mol%, preferably z < 30.0 mol%, and more preferably z < 25.0 mol%. In preferred embodiments, the content is 0.0 mol% < z < 40.0 mol%, preferably 5.0 mol% < z < 30.0 mol%, more preferably 8.0 mol% < z < 25.0 mol%.

[0044] In preferred embodiments, the content y of Co is > 0.0 mol%, more preferably y > 1.0 mol%, and even more preferably y > 3.0 mol%. In preferred embodiments, the content is y < 40.0 mol%, more preferably y < 30.0 mol%, and even more preferably y < 25.0 mol%. In preferred embodiments, the content is 0.0 mol% < y < 40.0 mol%, preferably 1.0 mol% < y < 30.0 mol%, more preferably 3.0 mol% < y < 25.0 mol%.

[0045] In preferred embodiments, D comprises at least one element of the group consisting of Al, B, Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, W, and Zn; preferably Al, B, Cr, Nb, S, Si, Ti, Y, and W.

[0046] In preferred embodiments, the content a of D is > 0.0 mol%, more preferably a > 0.25 mol%, and even more preferably a > 0.5 mol%. In preferred embodiments, the content is a < 2.0 mol%, preferably a < 1.75 mol%, and more preferably a < 1.5 mol%. In preferred embodiments, the content is 0.0 mol% < a < 2.0 mol%, preferably 0.25 mol% < a < 1.75 mol%, and more preferably 0.5 mol% < a < 1.5 mol%.

[0047] As understood by the skilled person, the secondary particles comprise a plurality of primary particles, preferably more than 20 primary particles, preferably more than 10 primary particles, most preferably more than 5 primary particles. A primary particle is a particle that is a single crystal or is formed from less than five and preferably at most three primary particles that are themselves single crystals. This can be observed by observing grain boundaries in suitable microscopy techniques such as scanning electron microscopy (SEM).

[0048] Embodiment 2

[0049] In a second embodiment, preferably according to embodiment 1, wherein the Zr content Zr A is b / (b+x+y+z) which is at least 0.10 mol% and at most 1.00 mol%. Preferably, the Zr content Zr A is b / (b+x+y+z) which is at least 0.20 mol% and at most 0.80 mol%. Most preferably, the Zr content Zr A is b / (b+x+y+z) which is at least 0.30 mol% and at most 0.70 mol%. In an alternative but even preferred embodiment, the Zr content Zr A is b / (b+x+y+z) which is at least 0.10 mol% and at most 1.50 mol%. Preferably, the Zr content Zr A is b / (b+x+y+z) which is at least 0.20 mol% and at most 1.00 mol%. Most preferably, the Zr content Zr A is b / (b+x+y+z) which is at least 0.30 mol% and at most 0.90 mol%.

[0050] In a preferred embodiment, the content b of Zr is at least 0.10 mol% and at most 1.00 mol% relative to M', more preferably at least 0.20 mol% and at most 0.80 mol% relative to M', most preferably at least 0.30 mol% and at most 0.70 mol% relative to M'.

[0051] In an alternative but even preferred embodiment, the content b of Zr is at least 0.10 mol% and at most 1.50 mol% relative to M', more preferably at least 0.20 mol% and at most 1.00 mol% relative to M', most preferably at least 0.30 mol% and at most 0.90 mol% relative to M'.

[0052] In a preferred embodiment, the Zr content Zr B is more than 0.25 mol%, preferably more than 0.50 mol%, most preferably more than 0.60 mol%. In a preferred embodiment, the Zr B is less than 2.0 mol%, preferably less than 1.5 mol%, more preferably less than 1.0 mol%. In a preferred embodiment, the Zr B is between 0.25 mol% and 2.0 mol%, preferably between 0.50 mol% and 1.5 mol%, most preferably between 0.60 mol% and 1.0 mol%. As understood by the skilled person, the Zr B is expressed as the molar fraction compared to the sum of the molar fractions of Co, Mn, Ni and Zr as measured by XPS analysis.

[0053] Embodiment 3

[0054] In a third embodiment, according to embodiments 1 to 2, the material has a secondary particle median size D50 of at least 2 pm, and preferably at least 5 pm, determined by laser diffraction particle size analysis.

[0055] Preferably, the material has a secondary particle median size D50 of at most 15 pm, and preferably at most 13 pm, determined by laser diffraction particle size analysis.

[0056] For example, but not limited to the present application, laser diffraction particle size analysis is performed by a Malvern Mastersizer 3000.

[0057] Embodiment 4

[0058] In a fourth embodiment, according to embodiments 1 to 3, the material has a carbon content of at least 600 ppm, preferably at least 650 ppm, more preferably at least 750 ppm and most preferably at least 900 ppm, determined by a carbon analyzer.

[0059] Preferably, the material has a carbon content of at most 5000 ppm, preferably at most 3000 ppm, more preferably at most 1500 ppm and most preferably at most 1100 ppm, determined by a carbon analyzer.

[0060] Embodiment 5

[0061] In a fifth embodiment, according to any one of embodiments 1 to 4, the thickness of Zr is > 10 nm. Preferably, the thickness is > 15 nm, and more preferably > 20 nm, determined by TEM-EDS measurement. Preferably, the thickness of Zr is < 100 nm, preferably the thickness is < 50 nm, more preferably the thickness is < 30 nm. Preferably, the thickness of Zr is between 10 nm and 100 nm, preferably between 15 nm and 50 nm, more preferably between 22 nm and 28 nm.

[0062] In the frame of the present application, the (minimal) thickness of the surface layer is defined as the shortest distance between a first point located at the periphery of the cross section of the particle and a second point located on a line defined between said first point and the center of geometry (or centroid) of said particle, wherein the difference in content of Zr at the position of the second point (Zr2) and at any position between said position of the second point and the center of said particle is 0.1 at%.

[0063] The Zr content at the second point position (Zr2) is constant: it can be higher than 0 at% and must be lower than or equal to 5.0% of the first Zr content (Zr1) at the first point position. Said second content Zr2 is equal to the Zr content at a third point position in said line (Zr3) and said third point is located at any position between the geometric center of the particle and the second point position.

[0064] In other words, the thickness of the surface layer corresponds to the minimum distance D, said minimum distance being defined as:

[0065] D (in nm) = L Zr1 - L Zr2

[0066] where L Zr1 is the first point position at the particle periphery, L Zr2 is the second point position on the line defined between said first point position and the geometric center of the particle, as shown in Figure 2

[0067] where the second content of Zr measured by TEM-EDS at the second point position L Zr2 is higher than or equal to 0 at% and lower than or equal to 5.0% of the first content of Zr (Zr1) measured at the first point position. Said second content of Zr (Zr2) is defined as:

[0068] Zr2 (in at%) Zr3 ± 0.1 at% and optionally Zr1 - Zr2 > 10.0 at%

[0069] ZG3 is the third content of Zr (in at%) at a third point position (L zr3 ) on said line, said third point being located at any position between the geometric center of the particle and the second point position L zr2 .

[0070] When Zr2 and Zr3 are higher than 0.0 at%, the second and third contents of Zr correspond to the content of Zr measured by TEM-EDS as a dopant in the core of the particle according to the application.

[0071] The TEM-EDS protocol is applied as follows:

[0072] 1) Extracting a cross-section TEM lamella of the lithium transition metal-based oxide particle by cutting the particle sample using a Ga ion beam in order to obtain a prepared sample.

[0073] ​2) The prepared sample (cross-section of the particle) is scanned from the outer edge of the surface layer to the center of the lithium transition metal-based oxide particle using TEM / EDS line scans in order to provide quantitative elemental analysis of the cross-section.

[0074] 3) The Zr content detected by EDS is normalized by the total atomic content of Ni, Mn, Co, and Zr in the scanned flake.

[0075] 4) The measured line scan of Zr / (Ni+Mn+Co+Zr) is then plotted as a function of linear distance in the cross-section of the particle.

[0076] The above steps 1) to 4) are repeated as many times as the particles to be analyzed.

[0077] The above TEM-EDS measurement is performed on at least one particle. When more than one particle is measured, a numerical average is performed on Zr / (Ni+Mn+Co+Zr).

[0078] For example, but not limited to the present application, TEM-EDS measurements are performed with a Tecnai G 2 F30 S-TWIN (FEI) with ELITE T 70 detector (EDAX).

[0079] As understood by the person skilled in the art, for any one of embodiments 1 to 5, Zr B is expressed as a molar fraction compared to the sum of the molar fractions of Co, Mn, Ni and Zr measured by XPS analysis; in particular, Zr B is the molar fraction of Zr measured in the region of the secondary particles of the positive electrode active material according to the present application, which is defined between a first point of the outer edge of the particle and a second point at a distance from the first point, the distance separating the first point from the second point being equal to the penetration depth of the XPS, the penetration depth D being comprised between 1.0 nm and 10.0 nm. In particular, the penetration depth is the distance along an axis perpendicular to a virtual line tangent to the outer edge and passing through the first point.

[0080] In the framework of the present application, the outer edge of the particle is the boundary or external limit that distinguishes the particle from its external environment.

[0081] Thus, the XPS analysis provides the atomic content of the elements in the uppermost layer of the particles, with a penetration depth of about 10.0 nm from the outer boundary of the particles. The outer boundary of the particles is also referred to as the "surface". In the frame of the present invention, at% means atomic percentage. The at% or "atomic percentage" in the expression of the concentration of a given element means how many percent of all atoms in the compound concerned are atoms of the element in question. Specifying "at%" is equivalent to the term "mol%" or "molar percentage". The XPS analysis is performed with a Thermo K-alpha+ spectrometer (Thermo Scientific), for example, but not limited to the present invention.

[0082] The present invention relates to the use of a positive electrode active material according to any one of the preceding embodiments 1 to 5 in a battery.

[0083] The present invention also comprises a method of manufacturing a positive electrode active material according to any one of the preceding embodiments 1 to 5, said method comprising the steps of:

[0084] - preparing a lithium transition metal-based compound,

[0085] - mixing said lithium transition metal-based compound with a Zr source, preferably a Zr alkoxide, in an alcoholic solvent containing lithium alkoxide, thereby obtaining a mixture, and

[0086] - removing the volatile phase, including the solvent, preferably by vacuum heating,

[0087] - heating the mixture in a furnace at a temperature of 350 °C to less than 500 °C, preferably up to 450 °C, in an oxidizing atmosphere for a time of 1 hour to 20 hours, to obtain a positive electrode active material powder according to the present invention.

[0088] In a preferred embodiment, the lithium transition metal-based compound is a lithium nickel-based oxide compound.

[0089] 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 at least one element of the group consisting of: Al, B, Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, W and Zn; preferably Al, B, Cr, Nb, S, Si, Ti, Y, W

[0090] Preferably, the lithium transition metal oxide powder used is also typically prepared according to a lithiation process, i.e. a process wherein a mixture of a transition metal precursor and a lithium source is heated at a temperature of preferably at least 500 °C. Typically, the transition metal precursor is prepared by co-precipitation of one or more transition metal sources, such as salts, and preferably sulphates of the M' elements Ni, Mn and / or Co, in the presence of an alkaline compound, such as an alkali hydroxide, e.g. sodium hydroxide and / or ammonia.

[0091] Preferably, the method further comprises the additional step of drying the mixture prior to heating the mixture, preferably by vacuum heating.

[0092] In a preferred embodiment of the method, the Zr source is a Zr-alkoxide, preferably a Zr-ethoxide, Zr-propoxide or Zr-butoxide, more preferably a Zr-propoxide. In a preferred embodiment, the Zr-alkoxide is mixed as a solid with the mixture. Alternatively and more preferably, the Zr-alkoxide is mixed as a solution with the slurry, wherein the solution comprises the Zr-alkoxide and a further alcohol, wherein the alkoxide group is a conjugate base of the further alcohol. For example, the Zr-alkoxide is a Zr-propoxide dissolved in propanol. Typically, the solution comprises 50 to 90 wt.% of the Zr-alkoxide, based on the total weight of the solution. An example of such a solution is a 70 wt.% Zr-propoxide solution in 1-propanol or an 80 wt.% Zr-butoxide solution in 1-butanol.

[0093] Preferably, the alcoholic solvent is methanol, ethanol, propanol or butanol, preferably ethanol.

[0094] The present application also comprises a solid-state battery comprising the positive electrode active material according to any one of the preceding embodiments 1 to 5, preferably the solid-state battery comprises a sulfide-based solid electrolyte, more preferably the sulfide-based solid electrolyte comprises Li, P and S. Typically, the following sulfur-containing compounds can be suitably used: Li6PS5CI (LPSCL), thio-LISICON (Li 3.25 Ge 0.25 P 0.75 S4), Li2S-P2S5-LiCI, LiC2S-SiS2, LiI-Li2S-SiS2, Li-P2S5-LiCI, LiC2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2SP2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, Li3PS4, Li7P3S 11 , LiI-Li2S-B2S3, Li3PO4-Li2S-SiS2, Li3PO4Li2S-SiS2, LiPO4-Li2S-SiS2, Li 10 GeP2S12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , and / or Li7P3S 11 . BRIEF DESCRIPTION OF DRAWINGS

[0095] Figure 1 a SEM image of secondary particles comprising a plurality of primary particles of CEX2.2. Dotted lines indicate regions that should be captured in order to obtain the average primary particle diameter.

[0096] Figure 1 b SEM image of CEX2.2 to obtain the average primary particle diameter.

[0097] Figure 1 c SEM image of EX1 to obtain the average primary particle diameter.

[0098] Figure 2 XPS spectra showing Zr peaks of EX1 and CEX2.2.

[0099] Figure 3 TEM-EDS analysis results of Zr / (Ni+Mn+Co+Zr) of EX1 (x-axis: distance, where 0 is the start of the surface layer, y-axis: elements in atomic ratio). DETAILED DESCRIPTION

[0100] In the drawings and the following detailed description, preferred embodiments of the application are described to enable a person having ordinary skill in the art to practice the application. While the application is described in conjunction with these preferred embodiments, it is understood that the application is not limited to these preferred embodiments. The application includes many alternatives, modifications and equivalents. It is also understood that other implementations of the application will become apparent to those of ordinary skill in the art from a reading of the following detailed description in conjunction with the associated drawings.

[0101] A) ICP analysis

[0102] The amount of Li, Ni, Mn, Co and Zr in the positive electrode active material powder is measured by inductively coupled plasma (ICP) method using an Agillent ICP 720-ES (Agilent Technologies, https: / / www.agilent.com / cs / library / brochures / 5990-6497EN 720-725 ICP-OES LR.pdf). A 2 gram sample of powder is dissolved in 10 mL of high purity hydrochloric acid (at least 37% by weight of HC1 relative to the total weight of the solution) in a conical flask. The flask can be covered with a glass sheet and heated on a hot plate at 380 °C until the precursor is completely dissolved. After cooling to room temperature, the solution in the conical flask is poured into a 250 mL volumetric flask. After that, the volumetric flask is filled with deionized water up to the 250 mL mark, then completely homogenized. An appropriate amount of solution is taken by pipette and transferred to a 250 mL volumetric flask for the 2nd dilution, at which time the internal standard and 10% hydrochloric acid are filled in the volumetric flask up to the 250 mL mark, then homogenized. Finally, this 50 mL solution is used for ICP measurement.

[0103] B) SEM (scanning electron microscope) analysis

[0104] The morphology of the positive electrode active material is analyzed by scanning electron microscopy (SEM) technique. The JEOL JSM7100F (https: / / www.jeolbenelux.com / JEOL-BV-News / jsm-7100f-thermal-field-emission-electron-microscope) is used to measure the particle size distribution of the positive electrode active material. The measurement is performed at 25 °C under a high vacuum environment of 9.6 x 10 -5 Pa.

[0105] C) Particle size

[0106] C1 ) Secondary particle size analysis

[0107] The particle size distribution (PSD) of the positive electrode active material powder was measured by laser diffraction particle size analysis using a Malvern Mastersizer 3000 with a Hydro MV wet dispersion accessory after each of the powder samples was dispersed in an aqueous medium (https: / / www.malvernpanalytical.com / en / products / product-range / mastersizer-range / mastersizer-3000#overview). To improve the dispersibility of the powder, sufficient ultrasonic radiation and stirring were applied, and an appropriate surfactant was introduced. D50 is defined as the particle size at 50% of the cumulative volume % distribution obtained from the measurement with the Malvern Mastersizer 3000 with Hydro MV.

[0108] C2) Primary particle size analysis

[0109] The diameter of the primary particles was calculated by using ImageJ software (ImageJ 1.52a, National Institutes of Health, USA) according to the following steps:

[0110] Step 1) Open the file containing the SEM image of the positive electrode active material at a magnification of 10,000x, where the image is taken at the center portion of the secondary particles. An example of such an image is shown in Figure la, where the dotted line shows the area to be captured corresponding to Figure 1 b the primary particles.

[0111] Step 2) Set the scale according to the SEM magnification.

[0112] Step 3) Draw a line after the primary particle edges using the polygon selection tool for at least 50 particles. If truncated, exclude the particles at the edge of the image.

[0113] Step 4) Measure the area of the stretched primary particles selected from the Set Measurements and Area box.

[0114] Step 5) Calculate the particle diameter of each measured area by assuming a spherical shape as follows and obtain the average primary particle diameter

[0115] for at least 50 particles.

[0116] D) X-ray photoelectron spectroscopy analysis

[0117] In the present invention, X-ray photoelectron spectroscopy (XPS) is used to analyze the surface of the positive electrode active material powder particles. In the XPS measurement, signals are collected from the first few nanometers (e.g., 1 nm to 10 nm) of the uppermost part of the sample (i.e., the surface layer). Therefore, all elements measured by XPS are contained in the surface layer.

[0118] For the surface analysis of the positive electrode active material powder particles, XPS measurements were performed using a Thermo K-alpha+ spectrometer (Thermo Scientific, https: / / www.thermofisher.com / order / catalog / product / IQLAADGAAFFACVMAHV).

[0119] Monochromatic Al Ka radiation (hu = 1486.6 eV) was used with a spot size of 400 pm and a measurement angle of 45°. A wide-range survey scan was performed at 200 eV pass energy to identify the elements present at the surface. The C1s peak with the maximum intensity (or centered) at a binding energy of 284.8 eV was used as the calibration peak position after data collection.

[0120] At least 10 precise narrow-range scans were then performed at 50 eV for each identified element to determine the precise surface composition.

[0121] Curve fitting was performed with CasaXPS version 2.3.19 PR1.0 (Casa Software, http: / / www.casaxps.com / ) using a Shirley-type background treatment and Scofield sensitivity factors. The fitting parameters are summarized in Table la. The line shape GL(30) is a Gaussian / Lorentzian product formula with 70% Gaussian line and 30% Lorentzian line. LA(a, b, m) is an asymmetric line shape, where a and b define the tail extension of the peak, and m defines the width.

[0122] Table 1 a. XPS fitting parameters for Ni2p3, Mn2p3, Co2p3 and Zr3d .

[0123]

[0124] For the Zr and Co peaks, constraints were set for each defined peak according to Table lb.

[0125] Table 1 b. XPS fitting constraints for peak fitting .

[0126]

[0127] The Zr surface content determined by XPS is expressed as the molar fraction of Zr in the surface layer of the particles divided by the total content of Ni, Mn, Co, and Zr in said surface layer, respectively. It is calculated as follows:

[0128]

[0129] E) Sulphide solid state battery testing

[0130] E1 ) Sulphide solid state battery preparation

[0131] Positive electrode preparation

[0132] To prepare the positive electrode, a slurry containing positive electrode active material powder, Li-P-S-based solid electrolyte, carbon (Super-P, Timcal), and binder (RC-10, Arkema) was mixed in a butyl acetate solvent in a formulation of 64.0:30.0:3.0:3.0 by weight ratio in an Ar-filled glove box. The slurry was cast on one side of an aluminum foil, and then the slurry-coated foil was dried in a vacuum oven to obtain a positive electrode.

[0133] The resulting positive electrode was punched into a diameter of 10 nm, in which the active material loading was about 4 mg / cm 2 .

[0134] Negative electrode preparation

[0135] To prepare the negative electrode, a Li foil (diameter 3 mm, thickness 100 pm) was placed at the center on top of an In foil (diameter 10 nm, thickness 100 pm) and pressed to form a Li-In alloy negative electrode.

[0136] Separator

[0137] To prepare a separator also having a solid electrolyte function in a battery, a Li-P-S-based solid electrolyte was granulated with a pressure of 250 MPa to obtain a pellet thickness of 100 pm.

[0138] Battery assembly

[0139] In an argon-filled glove box, a sulfide solid-state battery was assembled in the order from the bottom to the top: a positive electrode including an Al current collector having a coated portion on the top - a separator - a negative electrode having a Cu current collector on the Li side on the top. The stacked assembly was pressed together with a pressure of 250 MPa and placed in an external cage to prevent air exposure.

[0140] E2) Test method

[0141] ​​The test method is the conventional "constant cut-off voltage" test. The conventional battery test in the present invention follows the protocol shown in Table 2. Each battery is cycled at 60°C using a Toscat-3100 computer controlled constant current cycler station (from Toyo). The protocol uses a 1C current definition of 160 mA / g. Initial charge capacity (CQ1) and discharge capacity (DQ1) are measured at 0.1C C-rate in the following voltage range in constant current mode (CC):

[0142] - for CEX1.1, EX1, CEX2.1, CEX2.2, CEX3 and EX2, from 4.2 V to 2.5 V (Li / Li + ) or 3.6 V to 1.9 V (InLi / Li + ).

[0143] The irreversible capacity IRRQ is expressed in % as follows:

[0144]

[0145] Table 2. Cycle plan for sulphide solid state battery test method

[0146]

[0147] F) TEM (transmission electron microscope) analysis

[0148] To check the Zr distribution within the lithium transition metal-based oxide particles, cross-section TEM lamellas of the particles were prepared by Nova Nano SEM200 (FEI). The Ga ion beam was used with a 30 kV voltage and 30 pA-7 nA current. The size of the obtained etched sample was 5 x 8 pm and the thickness was 100 nm. Using the prepared sample (etched), the surface properties from the top to the center of the lithium transition metal-based oxide particle were analyzed by TEM and energy dispersive X-ray spectroscopy (EDS). TEM-EDS line scans were performed on a Tecnai G 2 F30 S-TWIN (FEI) with an ELITE T 70 detector (EDAX). The EDS analysis of the lithium transition metal-based oxide particle provides a quantitative elemental analysis of the cross-section. The Zr content was normalized by the total atomic fraction of Ni, Mn, Co and Zr.

[0149] The present invention is further illustrated by the following examples:

[0150] Comparative Example 1

[0151] CEX1 was obtained by solid-state reaction between a lithium source and a transition metal-based source run as follows:

[0152] 1) Coprecipitation: A transition metal-based oxidized hydroxide precursor with a metal composition of Ni 0.64 Mn 0.17 Co 0.20 is prepared by a coprecipitation process in a large continuous stirred tank reactor (CSTR) with mixed nickel manganese cobalt sulphates, sodium hydroxide and ammonia.

[0153] 2) Mixing: The transition metal-based oxidized hydroxide precursor and LiOH as lithium source are homogeneously mixed in an industrial blending equipment with a lithium to metal M' (Li / M') ratio of 1.03 to obtain a mixture.

[0154] 3) First heating: The mixture from step 2) is heated under an oxygen atmosphere at 830°C for 10 hours. The heated powder is crushed, classified and sieved in order to obtain an intermediate product.

[0155] 4) Second heating: The intermediate product from step 3) is heated under an oxygen atmosphere at 350°C for 6 hours in order to obtain CEX1.1 with M' comprising Ni, Mn and Co with a ratio of Ni:Mn:Co as obtained by ICP of 0.638:0.165:0.197. CEX1 has a D50 of 10 pm.

[0156] Optionally, a source of dopant can be added in the coprecipitation process in step 1) or in the mixing step in step 2) with the lithium source. For example, certain elements can be added as dopants to improve the electrochemical properties of the positive electrode active material.

[0157] Example 1

[0158] EX1 is obtained by a solid state reaction between a lithium source and a transition metal-based source run as follows:

[0159] 1) Coprecipitation: A transition metal-based oxidized hydroxide precursor with a metal composition of Ni 0.64 Mn 0.17 Co 0.200 is prepared by a coprecipitation process in a large continuous stirred tank reactor (CSTR) with mixed nickel manganese cobalt sulphates, sodium hydroxide and ammonia.

[0160] 2) Mixing: The transition metal-based oxidized hydroxide precursor and LiOH as lithium source are homogeneously mixed in an industrial blending equipment with a lithium to metal M' (Li / M') ratio of 1.03 to obtain a mixture.

[0161] 3) First heating: The mixture from step 2) is heated under an oxygen atmosphere at 830°C for 10 hours. The heated powder is crushed, classified and sieved in order to obtain an intermediate product.

[0162] 4) Wet mixing: Apply the following steps 4a) to step 4c) to introduce Zr into the positive electrode active material.

[0163] Step 4a) Zr solution preparation: Mix 0.6 mol% of Zr from Zr-propoxide (70 wt.% solution of Zr-propoxide in n-propanol solution), 1.2 mol% of lithium ethoxide powder and an ethanol solvent to form a solution, relative to the total molar content of Ni, Mn and Co in the intermediate product. The amount of ethanol solvent is 55 wt.% of the total weight of the specified intermediate product to be mixed in step 4b).

[0164] Step 4b) Mixing: Mix the intermediate product obtained from step 3) with the Zr solution prepared in step 4a) in a heatable reactor for 20 minutes.

[0165] Step 4c) Heating: Apply heat of 70 °C to the reactor in step 4b) while connecting the reactor to a vacuum pump to evaporate the volatile phase. The product obtained from this step is a dry powder.

[0166] 5) Second heating: Heat the dry powder from step 4c) at 350 °C for 6 hours under an oxygen atmosphere to obtain EX1 having M’ comprising Ni, Mn, Co and Zr in a ratio of Ni:Mn:Co:Zr of 0.635:0.163:0.196:0.006, as obtained by ICP. EX1 has a D50 of 10 pm.

[0167] Comparative Example 2

[0168] CEX2.1 was obtained by the same procedure as CEX1, except that the first heating temperature in step 3) was 860 °C.

[0169] CEX2.2 was obtained by the same procedure as EX1, except that the first heating temperature in step 3) was 860 °C.

[0170] Comparative Example 3

[0171] CEX3 was obtained by the same procedure as CEX1, except that the first heating temperature in step 3) was 795 °C.

[0172] Example 2

[0173] EX2 was obtained by the same procedure as EX1, except that the first heating temperature in step 3) was 795 °C.

[0174] Comparative Example 4

[0175] CEX4 was obtained by the same procedure as CEX1 except that the first heating temperature in step 3) was 750 °C.

[0176] Example 3

[0177] EX3 was obtained by the same procedure as EX1 except that the first heating temperature in step 3) was 750 °C.

[0178] Comparative Example 5

[0179] CEX5 was obtained by the same procedure as CEX1 except that the first heating temperature in step 3) was 750 °C.

[0180] Example 4

[0181] EX4 was obtained by the same procedure as EX1 except that the first heating temperature in step 3) was 750 °C.

[0182] Table 3. Summary of primary particle diameter, composition and corresponding electrochemical properties for examples and comparative examples .

[0183]

[0184] * Relative to the molar content of Ni, Mn, Co, and Zr

[0185] ** Due to Zr A was 0 and not applicable.

[0186] Table 3 summarizes the primary particle diameters, compositions, and corresponding electrochemical properties of the examples and comparative examples. The average primary particle diameters of EX1, EX2, EX3, and EX4 were 270 nm, 231 nm, 190 nm, and 192 nm, respectively. These average diameters were smaller than the average primary particle diameters of CEX2.1 and CEX2.2, which were 371 nm. SEM images of the primary particles of CEX2.2 and EX1 are shown in Figure 1 b and Figure 1 c , respectively. To obtain the average primary particle diameters, the images contained lines and numbers for determining the primary particles.

[0187] In Table 3, the results of XPS analysis of EX1 and CEX2.2 show the Zr atomic ratio (equivalent to the molar ratio) relative to the total atomic fraction of Ni, Mn, Co, and Zr (Zr B ). The table also compares the results with those of ICP. Zr BAbove 0 indicates that the Zr is present in the surface of the positive electrode active material associated with the XPS measurement, the signal of which is obtained from the first nanometers (e.g. 1 to 10 nm) of the uppermost part of the sample (i.e. the surface layer). On the other hand, the Zr atomic ratio obtained by ICP measurement comes from the whole particle. Therefore, a ratio (Zr B / Zr A ) above 1 indicates that the element Zr is mainly present on the surface of the positive electrode active material. A higher Zr B / Zr A value corresponds to a higher presence of Zr in the surface of the positive electrode active material. The Zr B / Zr A of EX1 is above the Zr B / Zr A of CEX2.2. A representation showing the XPS spectra of the Zr 3d5 and 3d3 peaks of CEX2.2 and EX1 is shown in Figure 2

[0188] Figure 3 A TEM-EDS measurement of EX1 is shown (x-axis: distance, where 0 is the start of the surface layer, y-axis: elements in atomic ratio). The Zr thickness obtained from the measurement is 25.8 nm.

[0189] The carbon content in the positive electrode active material after Zr treatment is higher compared to before treatment, which correlates with better electrochemical performance of the active material. The carbon originates from the Zr alkoxide compound used in the treatment.

[0190] A combination of an average primary particle diameter in the range of 170 nm to 340 nm and a Zr B / Zr A above 50.0, preferably above 100.0, can achieve the object of the present invention, i.e. to provide a positive electrode active material having an improved first charge capacity of at least 160 mAh / g in a solid-state battery.​

Claims

1. A positive electrode active material for solid-state batteries, wherein the positive electrode active material comprises Li, M’ and oxygen, wherein M’ comprises: - Ni, the content x of Ni is between 50.0 mol% and 75.0 mol% with respect to M’; - Co, the content y of Co is between 0.0 mol% and 40.0 mol% with respect to M’; - Mn, the content z of Mn is between 0.0 mol% and 40.0 mol% with respect to M’, - D, the content a of D is between 0.0 mol% and 2.0 mol% with respect to M’, wherein D comprises at least one element of Al, B, Ba, Ca, Cr, Fe, Mg, Mo, Nb, S, Si, Sr, Ti, Y, V, W and Zn, and - Zr, the content b of Zr is between 0.1 mol% and 5.0 mol% with respect to M’, - wherein x, y, z, a and b are measured by ICP, - wherein x + y + z + a + b is 100.0 mol%, wherein the positive electrode active material has a Zr content Zr A wherein the positive electrode active material has a Zr content Zr B wherein Zr B is determined by XPS analysis, wherein Zr B is expressed as a molar fraction compared to the sum of the molar fractions of Co, Mn, Ni and Zr as measured by XPS analysis,​ wherein the ratio Zr B / Zr A >50.0, wherein the carbon content is at least 600 ppm and at most 3000 ppm, the carbon content being determined by a carbon analyser, wherein the positive electrode active material comprises secondary particles having a plurality of primary particles, wherein the primary particles have an average diameter between 170 nm and 340 nm, the average diameter being determined by measuring the primary particle size in images taken by SEM.

2. Positive electrode active material according to claim 1, wherein the ratio Zr B / Zr A is at least 80.

3. Positive electrode active material according to claim 1 or 2, wherein the ratio Zr B / Zr A is at most 500.

4. The positive electrode active material according to claim 1 or 2, wherein x > 55.0 mol%.

5. The positive electrode active material according to claim 1 or 2, wherein x < 72.0 mol%.

6. The positive electrode active material according to claim 1 or 2, 0 mol% < y < 20 mol%.

7. The positive electrode active material according to claim 1 or 2, wherein b is at least 0.10 mol% and at most 1.00 mol% with respect to M’.

8. The positive electrode active material according to claim 1 or 2, wherein the secondary particle median size D50 is at least 2.0 pm and at most 15.0 pm, the secondary particle median size D50 being determined by laser diffraction particle size analysis.

9. The positive electrode active material according to claim 1 or 2, wherein the Zr thickness is at least 10 nm, the Zr thickness being determined by TEM-EDS measurement.

10. A method of manufacturing a positive electrode active material for solid-state batteries, wherein the positive electrode active material is the positive electrode active material according to any one of claims 1 to 9, the method comprising the following successive steps: - preparing a lithium transition metal-based oxide compound, - mixing the lithium transition metal-based oxide compound with a Zr alkoxide in an alcohol solvent containing lithium alkoxide, thereby obtaining a mixture, and - heating the mixture in a furnace at a temperature of 350 °C to less than 500 °C in an oxidizing atmosphere for a time of 1 hour to 20 hours, to obtain a positive electrode active material powder.

11. The method according to claim 10, wherein the method comprises the additional step of drying the mixture before heating the mixture.

12. The method according to claim 10, wherein the method comprises the additional step of drying the mixture by vacuum heating before heating the mixture.

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

14. The solid state battery according to claim 13, wherein the solid state battery comprises a sulfide-based solid electrolyte comprising Li, P and S.

15. Use of the battery according to claim 13 or 14 in an electric vehicle.

16. Use of the battery according to claim 13 or 14 in a hybrid electric vehicle.

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