A cathode active material for sodium batteries

Abstract

The present disclosure concerns a cathode active material for sodium batteries, comprising Na, M, and O, wherein M comprises relative to M: Ni in an atomic content x, wherein 0.10 ≤ x ≤ 0.60; Fe in an atomic content y, wherein 0.0 ≤ y ≤ 0.60; Mn in an atomic content z, wherein 0.10 ≤ z ≤ 0.60; Zn in an atomic content q, wherein 0.0 < q ≤ 0.10; Ti in an atomic content f, wherein 0.01 < f ≤ 0.20; Al in an atomic content f, wherein 0.0 ≤ a ≤ 0.020; wherein x, y, z, q, f and a are measured by ICP-OES, x+y+z+q+f+a is 1, the Na / M molar ratio is between 0.8 to 1.5; and wherein the cathode active material further comprises at least 0.15 % by weight of carbon.

Description

DescriptionTitleA CATHODE ACTIVE MATERIAL FOR SODIUM BATTERIESTechnical Field

[0001] The present invention relates to a cathode active material for sodium batteries and a method for the manufacture thereof.Description of Related Art

[0002] A major drawback of sodium batteries is the sensitivity of its cathode active materials to exposure to ambient air. 03 phase layered oxides of Ni, Fe, and Mn were found to provide high levels of capacity as well as high voltage levels. The performance of these materials relies heavily on the predominance of an 03 phase, which however readily transforms into a P2 phase during battery manufacture.

[0003] Such a phase transformation readily occurs upon prolonged storage of the cathode active material in particular in the presence of humidity and also upon exposure to ambient air. Storage of such materials may thus be severely limited.Summary

[0004] An objective of the present disclosure is to provide a cathode active material for sodium batteries, with improved storage stability.

[0005] In a first aspect of the present disclosure provides a cathode active material for sodium batteries, wherein the cathode active material comprises Na, M, and O, wherein M comprises:a. Ni in an atomic content x, wherein 0.10 < x < 0.60 relative to M,b. Fe in an atomic content y, wherein 0.0 < y < 0.60 relative to M,c. Mn in an atomic content z, wherein 0.10 < z < 0.60 relative to M,d. Zn in an atomic content q, wherein 0.0 < q < 0.10 relative to M,e. Ti in an atomic content f, wherein 0.01 < f < 0.20 relative to M,f. Al in an atomic content a, wherein 0.0 < a < 0.015 relative to M, wherein x, y, z, q, f and a are measured by ICP-OES, x+y+z+q+f+a = 1 , the Na / M molar ratio is between 0.8 to 1.5; and wherein the cathode active material further comprises at least 0.15 % by weight of carbon.

[0006] The inventors found that cathode active material of the present disclosure in particular shows little degradation upon storage, in particular under humid conditions. Such degradation may be established as the loss of 03 phase material.

[0007] A further aspect of the present disclosure refers to a method for the manufacture of cathode active material for sodium batteries, in particular a cathode active material according of the present disclosure in any of its embodiments or combination of embodiments. The method comprises- providing a starting material comprising Na, M’, and O, in particular wherein M’ comprises:i. Ni in an atomic content x2, wherein 0.10 < x2 < 0.60 relative to M’, ii. Fe in an atomic content y2, wherein 0.0 < y2 < 0.60 relative to M’, iii. Mn in an atomic content z2, wherein 0.10 < z2 < 0.60 relative to M, iv. Zn in an atomic content q2, wherein 0.0 < q2 < 0.10 relative to M’, v. Ti in an atomic content f2, wherein 0.01 < f2 < 0.20 relative to M’, wherein x2, y2, z2, q2, and f2 are measured by ICP-OES, x2+y2+z2+q2+f2 = 1 , the Na / M’ ratio is between 0.8 and 1.5;- blending the starting material with an alcohol as solvent and, optionally, an aluminum source, to obtain a first mixture;- drying the first mixture;- heating the first mixture up to a temperature Tmax of up to 600°C; and- cooling down the heated first mixture and optionally sieving to obtain the cathode active material.Figures

[0008] Figure 1 shows an SEM image of a cathode active material according to an embodiment of the present disclosure.

[0009] Figure 2 shows an SEM image of a cathode active material not according to an embodiment of the present disclosure.Detailed Description

[0010] "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.

[0011] As used herein, the term “and / or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items, can be employed. For example, if a composition is described as containing components A, B, and / or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

[0012] As used herein, a range of values “between X and Y” and “from X to Y” include the endpoints of X and Y.

[0013] 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 embodiments. On the contrary, the invention includes numerous alternatives, modifications, and equivalents as will become apparent from consideration of the following detailed description and accompanying drawings. Embodiments of the different aspects of the invention can be combined with one another, unless it is specifically mentioned otherwise.

[0014] The cathode active material of the present disclosure may in particular comprise secondary particles comprising a plurality of primary particles, in particular at least 20 primary particles. Such a polycrystalline material may provide a higher contact area with the electrolyte in a battery, thus increasing the battery’s performance. At least about 30% of the particles, more preferably at least about 50% of the particles, constituting the powder observed in a Scanning Electron Microscope (SEM) image may be such secondary particles. The number of primary particles constituting the monolithic particle is determined in a field of view of at least about 45 pm x at least about 60 pm (i.e. of at least about 2700 pm2), preferably of: at least about 100 pm xabout 100 m (i.e. of at least about 10,000 pm2). The particles in the image may be well distributed therefore avoiding overlap between particles. This can be achieved by pouring a small amount of powder sample to the adhesive attached on the SEM sample holder and blowing air to remove the excess powder. In the context of the present 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.

[0015] In the cathode active material of the present disclosure, Ni, Fe, Mn, Zn, and Ti may be uniformly distributed throughout the secondary and / or primary particles.

[0016] In an embodiment of the present disclosure, the cathode active material according to the first aspect, has a particle size distribution value D50 of at most 15 pm.

[0017] In an embodiment of the present disclosure, the cathode active material according to the first aspect, has a particle size distribution value D50 of at least 4pm.

[0018] In an embodiment of the present disclosure, the cathode active material according to the first aspect, has a particle size distribution value D50 ranging from about 5pm to about 7pm.

[0019] In a further implementation of the cathode active material according to the first aspect, the AIXPS / AIICP molar ratio is at least 50, advantageously at least 100, advantageously at least 150, wherein AIXPS is the fraction of Al relative to all elements of M as measured by X-ray photoelectron spectroscopy (XPS), and AIICP is the fraction of Al relative to all elements of M as measured by ICP-OES. In another embodiment of the present invention, the AIXPS / AIICP ratio may be up to 500.

[0020] In an embodiment of the present disclosure, the cathode active material comprises at most 0.50% by weight of carbon.

[0021] In an embodiment of the present disclosure, the cathode active material according to the first aspect comprises 0.20 < x < 0.55 relative to M. In another embodiment, 0.30 < x < 0.45 relative to M.

[0022] In an embodiment of the present disclosure, the cathode active material according to the first aspect comprises 0.0 < y < 0.20 relative to M. In another embodiment, y is 0 relative to M.

[0023] In an embodiment of the present disclosure, the cathode active material according to the first aspect comprises 0.20 < z < 0.60 relative to M. In another embodiment, 0.30 < z < 0.60 relative to M. In another embodiment, 0.40 < z < 0.60 relative to M.

[0024] In an embodiment of the present disclosure, the cathode active material according to the first aspect comprises 0.001 < q < 0.10 relative to M. In another embodiment, 0.01 < q < 0.10 relative to M. In another embodiment, 0.01 < q < 0.08 relative to M.

[0025] In an embodiment of the present disclosure, the cathode active material according to the first aspect comprises 0.05 < f < 0.20 relative to M. In another embodiment, 0.05 < f < 0.15 relative to M.

[0026] In an embodiment of the present disclosure, the cathode active material according to the first aspect comprises 0.0001 < a < 0.015 relative to M. In another embodiment, 0.001 < a < 0.010 relative to M. In another embodiment, 0.003 < a < 0.008 relative to M.

[0027] In an embodiment of the present disclosure, the cathode active material according to the first aspect comprises 0.20 < x < 0.55 relative to M; y is 0 relative to M; 0.20 < z < 0.60 relative to M; 0.001 < q < 0.10 relative to M; 0.05 < f < 0.20 relative to M; and 0.0001 < a < 0.010 relative to M.

[0028] In an embodiment of the present disclosure, the Na, M, and O content of the cathode active material is represented by the formula (I) NawNixiFeyiMnziZnqiTifiAlaiO2, (I), wherein 0.80 < w < 1.50; 0.10 < x1 < 0.60; 0.0 < y1 < 0.60; 0.10 < z1 < 0.60; 0.0 < q1 < 0.10; 0.01 <f1 < 0.20; 0.001 < a1 < 0.015; wherein x1 , y1 , z1 , q1 , f1 and a1 are measured by ICP-OES, and x1 +y1 +z1 +q1 +f1 +a1 is 1.

[0029] In an embodiment of the present disclosure, the cathode active material is according to formula (I), wherein 0.15 < x1 < 0.50, 0.15 < y1 < 0.50, 0.15 < z1 < 0.50, 0.2 < q1 < 0.08; and 0.05 < f1 < 0.15.

[0030] In an embodiment of the present disclosure, the cathode active material is according to formula (I), wherein 0.20 < x1 < 0.55; y1 is 0; 0.20 < z1 < 0.60; 0.001 < q1 < 0.10; and 0.05 < f1 < 0.20.

[0031] In an embodiment of the present disclosure, the cathode active material is according to formula (I), wherein 0.0001 < a1 < 0.015.

[0032] In an embodiment of the method of the present disclosure, the starting material comprises Na, M’, and 0, wherein M’ comprises:i. Ni in an atomic content x2, wherein 0.10 < x2 < 0.60 relative to M’, ii. Fe in an atomic content y2, wherein 0.0 < y2 < 0.60 relative to M’, iii. Mn in an atomic content z2, wherein 0.10 < z2 < 0.60 relative to M, iv. Zn in an atomic content q2, wherein 0.0 < q2 < 0.10 relative to M’, v. Ti in an atomic content f2, wherein 0.01 < f2 < 0.20 relative to M’, wherein x2, y2, z2, q2, and f2 are measured by ICP-OES, x2+y2+z2+q2+f2 = 1 , the Na / M’ ratio is between 0.8 and 1.5;

[0033] In an embodiment of the method of the present disclosure, the starting material comprises 0.20 < x2 < 0.55 relative to M’. In another embodiment, 0.30 < x2 < 0.45 relative to M’.

[0034] In an embodiment of the method of the present disclosure, the starting material comprises 0.0 < y2 < 0.20 relative to M’. In another embodiment, y2 is 0 relative to M’.

[0035] In an embodiment of the method of the present disclosure, the starting material comprises 0.20 < z2 < 0.60 relative to M’. In another embodiment, 0.30 < z2 < 0.60 relative to M’. In another embodiment, 0.40 < z2 < 0.60 relative to M’.

[0036] In an embodiment of the method of the present disclosure, the starting material comprises 0.001 < q2 < 0.10 relative to M’. In another embodiment, 0.01 < q2 < 0.10 relative to M’. In another embodiment, 0.01 < q2 < 0.08 relative to M’.

[0037] In an embodiment of the method of the present disclosure, the starting material comprises 0.05 < f2 < 0.20 relative to M’. In another embodiment, 0.05 < f2 < 0.15 relative to M’.

[0038] In an embodiment of the method of the present disclosure, 0.20 < x2 < 0.55 relative to M’; y2 is 0 relative to M’; 0.20 < z2 < 0.60 relative to M’; 0.001 < q2 < 0.10 relative to M’; 0.05 < f2 < 0.20 relative to M’.

[0039] In an embodiment of the method of the present disclosure, the starting material is represented by the formula (II) NawNixsFeysMnzsZnqsTifsC , (II), wherein 0.80 < w’ < 1.50; 0.10 < x3 < 0.60; 0.0 < y3 < 0.60; 0.10 < z3 < 0.60; 0.0 < q3 < 0.10; 0.01 < f3 <0.20; wherein x3, y3, z3, q3, and f3 are measured by ICP-OES, and x3+y3+z3+q3+f3 is 1.

[0040] In an embodiment of the method of the present disclosure, the starting material is according to formula (II), wherein 0.15 < x3 < 0.50, 0.15 < y3 < 0.50, 0.15 < z3 < 0.50, 0.2 < q3 < 0.08; 0.05 < f3 < 0.15.

[0041] In an embodiment of the method of the present disclosure, the starting material is according to formula (II), wherein 0.20 < x3 < 0.55; y3 is 0; 0.20 < z3 < 0.60; 0.001 < q3 < 0.10; and 0.05 < f3 < 0.20.

[0042] In an embodiment of the method of the present disclosure, the aluminum source to starting material ratio is chosen so as to obtain an Al content in the cathode active material ranging from 0.05 to 1.5 mol% with respect to the total molar contents of Ni, Mn, Zn, and Ti.

[0043] In an embodiment of the method of the present disclosure, the aluminum source is an aluminum alcoholate, in particular chosen from aluminum ethoxide and aluminum isopropoxide .

[0044] In an embodiment of the method of the present disclosure, the solvent is an alcohol, in particular chosen from ethanol and isopropanol.

[0045] In an embodiment of the method of the present disclosure, heating of the first mixture is performed under dry air, in particular performed under a flow of air having a dew point of less than -20°C, preferably less than -30°C.

[0046] In an embodiment of the method of the present disclosure, the starting material comprises secondary particles comprising a plurality of primary particles. Starting material secondary particles may in particular comprise at least 20 primary particles.

[0047] In an embodiment of the method of the present disclosure, Tmax ranges from 150°C to 500°C.

[0048] In an embodiment of the method of the present disclosure, after heating the first mixture up to a temperature Tmax, and before cooling, the first mixture is maintained at Tmax for a duration of at least 2 hours and of at most 10 hours.

[0049] The present disclosure further concerns a sodium battery comprising a cathode active material according to the present disclosure in any embodiment or combination of embodiments.

[0050] The present disclosure further concerns the use of a battery comprising a cathode active material according to the present disclosure in any embodiment or combination of embodiments 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 plugin 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, a defense system, and a medical device.Characterization

[0051] Powder X-ray diffraction (PXRD) - To identify the crystalline phases of the prepared materials, powder XRD patterns were collected in the 29 range of 10-130° using Co Ka X-rays (1.79 A at 45 kV and 40 mA) on an D8 X-ray diffractometer (Broker) with acquisition time 11 min. The samples were tested in a sample holder in a dry room (-34°C DP), to prevent exposure to moisture. Rietveld refinement was performed with the following phases: 03-type structure with space group R3m, undersodiated phase P2 (P 63 / m m c) and metal oxide (Fm-3m), which corresponds to Nio.8Zno.2O phase due to lattice parameter a=4.2 A. For the sample after moistures exposure the following phases were used for the refinement: 03 (R-3m), P3 (R3m) and metal oxide (Fm-3m).

[0052] Scanning Electron Microscopy (SEM) - The morphology of positive electrode active materials is analyzed by a Scanning Electron Microscopy (SEM) technique. The measurement is performed using a JEOL JSM-F100 under a high vacuum environment of 8x1 O’6Pa at 25 °C. 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 dry air to remove the excess powder. Figure 1 shows the SEM image of EX1. Figure 2 shows the SEM image of CEX1.

[0053] Particle size distribution (PSD) - The particle size of the positive electrode active material powders is measured using a Malvern Mastersizer 3000 equipped with an Aero S dry dispersion accessory. The powders are introduced into the instrument through a dry feeder system, where they are dispersed in a stream of compressed air.The D50 value, defined as the particle size at which 50% of the cumulative volume is smaller and 50% is larger. Meanwhile, the span is defined as (D90 - D10) / D50.

[0054] Inductively Coupled Plasma (ICP) - The composition of a positive electrode active material powder is measured by the inductively coupled plasma (ICP) method using an Agilent 720 ICP-OES. 1 gram of powder sample is dissolved into 50 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 watch glass and heated on a hot plate at 380 °C until the powder is completely dissolved. After cooling to room temperature, the solution from the Erlenmeyer flask is poured into a first 250 mL volumetric flask. Afterwards, the first volumetric flask is filled with deionized water up to the 250 mL mark, followed by a complete homogenization process (1stdilution). An appropriate amount of the solution from the first volumetric flask is taken out by a pipette and transferred into a second 250 mL volumetric flask for the 2nddilution, where the second volumetric flask is filled with an internal standard element and 10% hydrochloric acid up to the 250 mL mark and then homogenized. Finally, this solution is used for ICP measurement.

[0055] 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. 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 a 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. Curve fitting is done with CasaXPS Version 2.3.19PR1.0 using a Shirley-type background treatment and Scofield sensitivity factors. The fitting parameters are according to Table 1. Line shape GL(30) is the Gaussian / Lorentzian product formula with 70%Gaussian line and 30% Lorentzian line. LA(a, (3, m) is an asymmetric line-shape where a and [3 define tail spreading of the peak and m define the width.

[0056] Table 1 XPS fitting parameter for B1s.Sensitivity Fitting rangeElement Defined peak(s) Line shape factor (eV)72.0 ± 0.1 - Al 0.72 AI2p peak GL(30)80.0 ± 0.1

[0057] Carbon Analysis - The contents of carbon of the cathode materials are advantageously measured by Horiba EMIA-320V Carbon / Sulfur analyzer. Between about 0.5g and about 1 g of positive electrode active material sample is placed in a ceramic crucible in a high frequency induction furnace. Then, about 2g of accelerators, for example 1.5 g of Tungsten and 0.3 g of Tin, are added into the crucible. The sample is heated at a programmable temperature, for example up to 1200°C. Gases produced during the combustion are then analyzed by four Infrared detectors. The analysis of low and high CO2 and CO determines carbon concentration.

[0058] Exposure test - The storage stability is tested by storing the positive electrode active material in a controlled atmosphere humidity chamber (HCP50, Memmert), which is set at 30°C and 55% relative humidity. The test is conducted for up to 72 hours with periodic sampling of the material for physical characterization.

[0059] Coin cell assembly - The coin cell is assembled inside of an argon-filled glovebox to prevent contamination. 2 separators (Glass Fiber, Whatman) are placed between the positive electrode and a piece of sodium foil, which serves as the negative electrode. An electrolyte solution comprising 0.6 M NaPF6 in polyethylene carbonate (PC) with 2% FEC additive is dropped between the separator and the electrodes. The coin cell is then sealed to prevent electrolyte leakage, completing the assembly process.

[0060] Cycling protocol - The tests for discharge capacity (DQ) and irreversible capacity (Qirr) are performed using coin cells with electrodes consisting of 92 wt% of the cathode active material described in this invention. The electrode loading is approximately 11 mg / cm2. The discharge capacity for the first cycle (DQ1) is measured within the voltage range of [4.2 V - 2.2 V] at a rate of 0.1 C (expressed in mAh / g) at a temperature of 25°C.

[0061] Example 1 - A positive electrode active material labelled as EX1 is prepared according to the following steps:a. Step 1) Nio.45Mno.55(OH)2 is mixed with NaOH, ZnO, and TiO2 in an Eirich mixer at 4000 rpm for 2 minutes in a dry room (-34°C dew point).

[0062] Step 2) The mixture from step 1) is heated at 950 °C for 12 h under dry air atmosphere and then cooled to 80°C at a cooling rate of 1°C / min. The resulting heated product is then sieved using a 53 pm mesh to obtain an intermediate product having a formula of Nao.85[Nio.38Mno.48Zno.o4Tio.io]02.

[0063] Step 3) The intermediate product from step 2) is mixed with aluminium isopropoxide which is dissolved in ethanol, so as to obtain a content of Al of 0.5 mol% with respect to the total molar contents of Ni, Mn, Zn, and Ti, to obtain a second mixture. The flask containing the mixture is transferred into a water bath. Then, the solution is stirred under N2 atmosphere for about 60 to 90 minutes, and the water bath is set to 45°C to evaporate the solvent gradually.a. Step 4) The wet powder from Step 3) is dried in a vacuum oven at 120°C overnight to remove the residual solvent from the mixture.b. Step 5) The resulting powder from Step 4) is transferred into an alumina crucible and heated to a 2ndheating temperature 350°C under oxygen for 6 h with a ramping rate of 5°C / min. Then, the heated powder is cooled to 80°C at a cooling rate of 1°C / min. The resulting powder is then sieved using a 53 pm mesh to obtain the positive electrode active material labelled as EX1

[0064] Example 2 - A positive electrode active material labelled as EX2 is prepared according to the following steps:a. Step 1) Nio.45Mno.55(OH)2 is mixed with NaOH, ZnO, and TiO2 in an Eirich mixer at 4000 rpm for 2 minutes in a dry room (-34°C dew point).

[0065] Step 2) The mixture from step 1) is heated at 950 °C for 12 h under dry air atmosphere and then cooled to 80°C at a cooling rate of 1°C / min. The resulting heated product is then sieved using a 53 pm mesh to obtain an intermediate product having a formula of Nao.85[Nio.38Mno.48Zno.o4Tio.io]02.a. Step 3) The intermediate product from step 2) is dissolved in ethanol. The flask containing the mixture is transferred into a water bath. Then, the solutionis stirred under N2 atmosphere for 60 - 90 minutes and the water bath is set to 45°C to evaporate the solvent gradually.b. Step 4) The wet powder from Step 3) is dried in a vacuum oven at 120°C overnight to remove the residual solvent from the mixture.c. Step 5) The resulting powder from Step 4) is transferred into an alumina crucible and heated to a 2nd heating temperature of 350°C under oxygen for 6 h with a ramping rate of 5°C / min. Then, the heated powder is cooled to 80°C at a cooling rate of 1°C / min. The resulting powder is then sieved using a 53 pm mesh to obtain the positive electrode active material labelled as EX2

[0066] The example, EX2, is subjected to further analysis.

[0067] Comparative example 1 - A positive electrode active material labelled as CEX1 is prepared according to the following steps:a. Step 1) Nio.45Mno.55(OH)2 is mixed with NaOH, ZnO, and TiO2 in Elrich mixer at 4000 rpm for 2 minutes in a dry room (-34°C dew point).

[0068] Step 2) The mixture from step 1) is heated at 950 °C for 12 h under dry air atmosphere and then cooled to 80°C at a cooling rate of 1°C / min. The resulting heated product is then sieved using a 53 pm mesh to obtain a positive electrode active material having a formula of Nao.85[Nio.38Mno.48Zno.o4Tio.io]02 labelled as CEX1.

[0069] The example, CEX1 , is subjected to further analysis.

[0070] Comparative example 2 - A positive electrode active material labelled as CEX2 is prepared according to the following steps:a. Step 1) Nio.45Mno.55(OH)2 is mixed with NaOH, ZnO, and TiO2 in Elrich mixer at 4000 rpm for 2 minutes in a dry room (-34°C dew point).

[0071] Step 2) The mixture from step 1) is heated at 950 °C for 12 h under dry air atmosphere and then cooled to 80°C at a cooling rate of 1°C / min. The resulting heated product is then sieved using a 53 pm mesh to obtain an intermediate product having a formula of Nao.85[Nio.38Mno.48Zno.o4Tio.io]02.a. Step 3) The powder from Step 2) is heated again at a second heating temperature of 350°C under oxygen for 6 h with a ramping rate of 5°C / min. Then, the heated powder is cooled to 80°C at a cooling rate of 1°C / min. Theresulting powder is then sieved using a 53 pm mesh to obtain the positive electrode active material labelled as CEX2.

[0072] The pristine example, CEX2, is subjected to further analysis. And some amount of the pristine example is subjected to a moisture exposure test and then further subjected to further analysis.

[0073] The summary of the preparation process for the examples and comparative example can be found in Table 2.

[0074] Table 2. Summary of the coating process for the preparation of positive electrode active material.Al coating Ethanol 2ndHeating 2ndHeating ID Core(mol%) solvent temperature (°C) time (hour) Nao.85[Nio.38Mno.48Zno.o4Tio.io]0EX1 0.5 Yes 350 62Nao.85[Nio.38Mno.48Zno.o4Tio.io]0EX2 - Yes 350 62Nao.85[Nio.38Mno.48Zno.o4Tio.io]0CEX1 - No - - 2Nao.85[Nio.38Mno.48Zno.o4Tio.io]0CEX2 - No 350 62

[0075] Table 3. Composition of examples and comparative examples from ICP and XPS and their corresponding electrochemical properties from coin-cell test of the pristine examples:ICP XPS** XPS** / ICP* 0.1C 1C DQ1ID Ni* Mn* Zn* Ti* Al* AIXPS decay decay AIXPS / AI (mAh / g)(mol%) (mol%) (mol%) (mol%) (mol%) (mol%) (%) (%) EX1 38.3 46.4 4.9 9.9 0.5 93.2 186.4 155.77 12.14 26.01 EX2 38.6 46.7 4.9 9.9 - - - 155.04 14.65 27.52 CEX1 38.5 46.7 4.9 9.9 - - - 156.42 15.73 29.40 CEX2 38.5 46.7 4.9 9.9 - - - 153.50 16.72 28.80*Calculated versus the total mo ar fraction of Ni, Mn, Zn, Ti, and Al, as analysed by IC P-OES; ** Calculated versus the total molar fraction of Ni, Mn, Zn, Ti, and Al, as analysed by XPS.

[0076] Table 4. Summary of the exposure test result and the corresponding properties of examples and comparative examples.Na occupationD50 (pm) Carbon (wt%) Crystallite size (nm) fractionIDBefore After 72h Before After 72h Before After 72h Before After 72h exposure exposure exposure exposure exposure exposure exposure exposure EX1 6.10 6.00 0.19 0.34 0.83 0.76 298 196 EX2 5.51 5.45 0.23 0.40 0.82 0.76 298 183 CEX1 6.44 9.36 0.07 1.33 0.85 0.50 287 32 CEX2 6.19 8.11 0.09 0.25 0.86 0.53 286 275

[0077] Table 5 - 03 weight percentage, after Oh, 3h, and 72h exposure test03 (wt%)Oh 3h 72hEX1 97.92 99.10 98.25 EX2 97.92 98.01 98.20 CEX1 98.02 98.36 52.92 CEX2 98.91 96.58 96.94

[0078] As can be seen from Table 5, EX1 and EX2, having a higher carbon content, show significantly higher 03 weight percentage after 72h exposure to humid atmosphere, thus showing improved stability. EX1 , with Al coating, is even more stable than EX2 without Al coating.

Claims

Claims

1. A cathode active material for sodium batteries, wherein the cathode active material comprises Na, M, and 0, wherein M comprises:a. Ni in an atomic content x, wherein 0.10 < x < 0.60 relative to M,b. Fe in an atomic content y, wherein 0.0 < y < 0.60 relative to M,c. Mn in an atomic content z, wherein 0.10 < z < 0.60 relative to M, d. Zn in an atomic content q, wherein 0.0 < q < 0.10 relative to M,e. Ti in an atomic content f, wherein 0.01 < f < 0.20 relative to M,f. Al in an atomic content a, wherein 0.0 < a < 0.015 relative to M, wherein x, y, z, q, f and a are measured by ICP-OES, x+y+z+q+f+a is 1, the Na / M molar ratio is between 0.8 to 1.5; and wherein the cathode active material further comprises at least 0.15 % by weight of carbon.

2. A cathode active material according to claim 1 , having a ratio AIXPS / AIICP of at least 50, wherein AIXPS is the fraction of Al relative to all elements of M as measured by X-ray photoelectron spectroscopy, and AIICP is the fraction of Al relative to all elements of M as measured by ICP-OES.

3. A cathode active material according to claim 1 or 2, having a particle size distribution value Dso of at most 15 pm.

4. A cathode active material according to any of the claims 1 to 3, wherein 0.001 < a < 0.010 relative to M.

5. A cathode active material according to any of the claims 1 to 4, wherein the Na, M, and O content of the cathode active material, is represented by the formula (I) NawNixiFeyiMnziZnqiTifiAlaiO2 (I), wherein 0.80 < w < 1.50; 0.10 < x1 < 0.60; 0.0 <y1 < 0.60; 0.10 <z1 < 0.60; 0.0 < q1 < 0.10; 0.01 <f1 < 0.20; 0.0 < a1 < 0.015; wherein x1, y1, z1, q1, f1 and a1 are measured by ICP-OES, and x1+y1+z1+q1+f1+a1 = 1.

6. A cathode active material according to claim 5, wherein 0.15 < x1 < 0.50, 0.15 < y1 < 0.50, 0.15 < z1 < 0.50, 0.2 < q1 < 0.08; 0.05 < f1 < 0.15.

7. A cathode active material according to claim 5 or 6, wherein 0.001 < a1 < 0.010.

8. A method for manufacturing a cathode active material for sodium batteries according to any of the claims 1 to 7, wherein the method comprises the following steps:- providing a starting material comprising Na, M’, and 0, wherein M’ comprises:i. Ni in an atomic content x2, wherein 0.10 < x2 < 0.60 relative to M’, ii. Fe in an atomic content y2, wherein 0.0 < y2 < 0.60 relative to M’, iii. Mn in an atomic content z2, wherein 0.10 < z2 < 0.60 relative to M, iv. Zn in an atomic content q2, wherein 0.0 < q2 < 0.10 relative to M’, v. Ti in an atomic content f2, wherein 0.01 < f2 < 0.20 relative to M’, wherein x2, y2, z2, q2, and f2 are measured by ICP-OES, x2+y2+z2+q2+f2 = 1 , the Na / M’ ratio is between 0.8 and 1.5;- mixing the starting material with an alcohol as solvent, and optionally with an Al source to obtain a first mixture;- drying the first mixture;- heating the first mixture up to a temperature Tmax of up to 600°C; and- cooling down the heated first mixture to obtain the cathode active material.

9. The method according to claim 8, wherein the alcohol is selected from ethanol and isopropanol.

10. The method according to claim 8 or 9, wherein the aluminum source is an aluminum alcoholate, in particular selected from aluminum ethoxide and aluminum isopropoxide .

11. Method according to any of the claims 8 to 10, wherein heating of the first mixture is performed under dry air.

12. Method according to any of the claims 8 to 11 , wherein Tmax ranges from 150°C to 500°C.

13. Method according to any of the claims 8 to 12, wherein the aluminum source to starting material ratio is chosen so as to obtain an Al content in the cathode active material ranging from 0.05 to 1.5 mol% with respect to the total molar contents of Ni, Mn, Zn, and Ti.

14. A sodium battery comprising a cathode active material according to any of the claims 1 to 7.

15. The use of a sodium battery according to claim 14, 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, a defense system, and a medical device.

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