Sodium metal oxide material for secondary batteries and method of preparation

Abstract

The invention relates to a method of preparing a sodium metal oxide material comprising Na.sub.xM.sub.yCo.sub.zO.sub.2-δ, where M is one or more of the following elements: Mn, Cu, Ti, Fe, Mg, Ni, V, Zn, Al, Li, Sn, Si, Ga, Ge, Sb, W, Zr, Nb, Mo, Ta, 0.7≤x≤1.3, 0.9≤y≤1.1, 0≤z<0.15, 0≤δ≤0.2 and wherein the average length of primary particles of said sodium metal oxide material is between 2 and 10 μm, preferably between 5 and 10 μm. The invention also relates to such a material.

Claims

1. A method of preparing a sodium metal oxide material comprising Na.sub.xM.sub.yCo.sub.zO.sub.2-δ, where M is one or more of the following elements: Mn, Cu, Ti, Fe, Mg, Ni, V, Zn, Al, Li, Sn, Si, Ga, Ge, Sb, W, Zr, Nb, Mo, Ta, 0.7≤x≤1.3, 0.9≤y≤1.1, 0≤z<0.15, 0≤δ<0.2 and wherein the average length of primary particles of said sodium metal oxide material is between 2 and 10 μm, said method comprising the steps of: a) mixing precursor materials comprising sodium salt and a salt of at least one of the following elements: Mn, Cu, Ti, Fe, Mg, Ni, V, Zn, Al, Li, Sn, Si, Ga, Ge, Sb, W, Zr, Nb, Mo, Ta, to a mixed precursor, wherein the mixed precursor comprises carbonate; b) placing the mixed precursor in an oven and heating the oven to a temperature of up to a temperature of between 800 and 1000° C. to provide the sodium metal oxide material; and c) cooling the sodium metal oxide material to room temperature in an atmosphere with less than 100 ppm CO.sub.2; wherein step b) comprises the sub-steps of: b1) heating the oven to a first temperature T1 between 900 and 1000° C.; b2) maintaining the temperature of the oven at the first temperature T1 until a specific phase distribution between P2 and O3 phases is achieved; b3) cooling the oven to a second temperature T2, where T2 is between 800 and 950° C. and wherein T2 is 50-150° C. lower than T1; and b4) maintaining the temperature of the oven at the second temperature T2 until the sodium metal oxide material is substantially carbonate free.

2. A method according to claim 1, wherein the mixing of precursor materials of step a) is in a dispersion.

3. A method according to claim 1, wherein the method further comprises step a2) of drying the mixed precursor to a mixed precursor having a moisture content between 2 and 15 wt %.

4. A method according to claim 1, wherein the atmosphere in the oven during step a) and/or during step b) is atmospheric air.

5. A sodium metal oxide material for an electrode of a secondary battery prepared by mixing precursor materials to a mixed precursor material, where the mixed precursor material comprise carbonate; heat treating the mixed precursor material to provide the sodium metal oxide material, where a heat treatment of said dried mixed precursor material to a temperature of 975° C. until the sodium metal oxide material is substantially carbonate free and subsequent cooling would provide a single phase sodium metal oxide material, wherein said mixture of precursor materials has been heat treated according to steps b1)-b4) of the process of claim 1, thereby rendering said sodium metal oxide material as a two phase material comprising the P2 and O3 phases, where said sodium metal oxide material has a tap density of between 1.5 and 2.2 g/cm.sup.3.

6. A sodium metal oxide material for an electrode of a secondary battery, said sodium metal oxide material being a two phase material comprising the P2 and O3 phases, where said sodium metal oxide material has a tap density of between 1.5 and 2.2 g/cm.sup.3.

7. A sodium metal oxide material according to claim 5, said sodium metal oxide material comprising: Na.sub.xM.sub.yCo.sub.zO.sub.2-δ, where M is one or more of the following elements: Mn, Cu, Ti, Fe, Mg, Ni, V, Zn, Al, Li, Sn, Si, Ga, Ge, Sb, W, Zr, Nb, Mo, Ta, and where 0.7≤x≤1.3, 0.9≤y≤1.1, 0≤z<0.15, 0≤δ<0.2.

8. A sodium metal oxide material according to claim 7, wherein M is one or more of the following elements: Mn, Cu, Ti, Fe, Mg, Ni, V, Zn, Al, Li, Sn, Si, Ga, Ge, Sb.

9. A sodium metal oxide material according to claim 7, wherein M is one or more of the following elements: Mn, Cu, Ti, Fe, Mg, Ni, V, Zn, Al, Li, Sn.

10. A sodium metal oxide material according to claim 7, wherein M comprises Ni and at least one further metal chosen from the group of: Mn, Cu, Ti, Fe, Mg.

11. A sodium metal oxide material according to claim 7, wherein M comprises Ni and Mn.

12. A sodium metal oxide material according to claim 7, wherein M comprises Ni, Mn, Mg and Ti.

13. A sodium metal oxide material according to claim 7, wherein the average length of primary particles of said sodium metal oxide material is between 2 and 10 μm.

14. A sodium metal oxide material according to claim 7, wherein z=0.

15. A sodium metal oxide material according to claim 7, wherein the primary particles have a length and a thickness, where the thickness is smaller than the length, and where the average thickness of primary particles is between 1.0 and 4.0 μm.

16. A sodium metal oxide material according to claim 7, wherein the sodium metal oxide material comprises 20-40 wt % P2 phase and 60-80 wt % O3 phase.

17. A sodium metal oxide material according to claim 7, wherein the tap density of said sodium metal oxide material is between 1.7 and 2.0 g/cm.sup.3.

18. A sodium metal oxide material according to claim 7, wherein the BET area is between 0.3 and 1 m.sup.2/g.

Description

SHORT DESCRIPTION OF THE FIGURE

[0043] FIG. 1 is a schematic drawing of a P2 type material with flake like primary particles.

DETAILED DESCRIPTION OF THE FIGURE

[0044] FIG. 1 is a schematic drawing of a P2 type material with flake like primary particles, such as the P2 type material Na.sub.2/3Mn0.7Fe0.1Mg0.1O.sub.2. It is seen from FIG. 1, that the primary particles typically have a platelet-like morphology with clear facets, where the largest dimension or an equivalent diameter of the primary particles is clearly larger than the thickness of the primary particles. For a few of the primary particles, the length L or the thickness T has been indicated in FIG. 1. The primary particles are about 1-3 μm in diameter or length and 100-500 nm in thickness. FIG. 1 illustrates that particles have a largest dimension, the length, and a smallest dimension, the thickness. FIG. 1 also illustrates that for some particles, the length or the thickness may not be discernible. In this case only the thickness or the length of the particle is included in a determination of the average length and thickness of the particles in the sample.

[0045] The length L of a primary particle is thus the greatest of three dimensions of the primary particle and the thickness of the primary particle is the smallest of the three dimensions thereof.

EXAMPLE

Preparation of Sodium Metal Ion Material:

[0046] Precursor materials in the form of a physical mixture of raw material comprising carbonates of Na and Ni and at least one of the elements Mn, Cu, Ti, Fe, and Mg, are mixed in an aqueous dispersion and subsequently spray dried to a powder. The spray dried and mixed precursor material is placed in a sagger. The bulk density of the spray dried and mixed precursor material is about 0.7-1.0 g/cm3 and the sagger is filled so that the bed height of spray dried and mixed precursor material is higher than 35 mm. The mixed and spray dried precursor materials have a moisture content between 2 and 15 wt %. The naggers with 20-22 kg of mixed and spray dried precursor materials containing in total about 0.4-3.3 L of water are loaded into an oven. The oven used in this case is an electrically heated chamber furnace with five-side heating from Nabertherm (LH 216 with controller C 440) modified with controllable gas inlets.

[0047] Subsequently, a heat treatment program of the oven is started and the oven is heated up to oven top temperature of 500° C. with a ramp of 1-5 C.°/min without any gas flow through the oven. At these conditions, moisture can be observed condensing on the outside of the oven walls because it is not completely gas tight. When the temperature in the top of the oven reaches about 500° C., the powder reaches 280 C-320 C and the carbonates start decomposing in the saturated moisture atmosphere. At this point, a flow of air of between 20 and 100 L/min is started from the bottom of the oven to the top and it is gradually heated to 900-1000° C. with a ramp of between 1-5° C./min.

[0048] After several hours, such as between 5 and 20 hours, the oven is cooled in a flow of CO.sub.2-free air of 1-100 L/min. When the oven has been cooled to about 500° C., nitrogen can be used as cooling medium until the oven reaches room temperature if a higher flow of nitrogen is available.

[0049] While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.