O3/P2 MIXED PHASE SODIUM-CONTAINING DOPED LAYERED OXIDE MATERIALS

Abstract

The invention relates to O3/P2 mixed-phase sodium-containing doped layered oxide materials which comprise a mixture of a first phase with an O3-type structure and a second phase with a P2-type structure; wherein the O3:P2 mixed-phase sodium-containing doped layered oxide material has the general formula: Na.sub.aA.sub.bM.sup.1.sub.c M.sup.2 M.sup.3.sub.eM.sup.4.sub.f M.sup.5 O.sub.2±δ. The invention also provides a process for making such O3/P2 mixed-phase sodium-containing doped layered oxide materials, and use applications therefor.

Claims

1. An O3/P2 mixed-phase sodium-containing doped layered oxide material which comprises a mixture of phases, wherein a first phase has one or more O3-type structures and a second phase has one or more P2-type structures; further wherein the O3/P2 mixed-phase sodium-containing doped layered oxide material has the general formula:
Na.sub.aA.sub.bM.sup.1.sub.cM.sup.2.sub.dM.sup.3.sub.eM.sup.4.sub.fM.sup.5.sub.gO.sub.2±δ; wherein: A is an alkali metal selected from at least one of lithium and potassium; M.sup.1 is one or more metals with an average oxidation state of 2+ selected from nickel, iron, manganese, cobalt, copper, magnesium, calcium and zinc; M.sup.2 is one or more metals with an average oxidation state of 4+ selected from manganese, titanium and zirconium; M.sup.3 is one or more metals with an average oxidation state of 2+ selected from magnesium, calcium, copper, zinc and cobalt; M.sup.4 is one or more metals with an average oxidation state of 4+ selected from manganese, titanium and zirconium; and M.sup.5 is one or more metals with an average oxidation state of 3+ selected from aluminum, iron, cobalt, molybdenum, chromium, vanadium, scandium and yttrium; wherein: a>0; 0≤b<0.5 a>b; 0.75<(a+b)≤1.0; 0≤c<0.5; d≥0; f≥0; at least one of d and f is >0; e>0; 0≤g<0.5; 0≤δ≤0.1; wherein: a, b, c, d, e, f and g are chosen to maintain electroneutrality; and wherein the O3/P2 mixed-phase sodium-containing doped layered oxide material is neither a material with the general formula Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.100Ti.sub.0.117O.sub.2 which comprises a mixture of phases in which a first phase has an O3-type structure and a second phase has a P2-type structure, wherein the amount of the first phase is 63% and the amount of the second phase is 37%, based on the combined total number of moles of the first and second phases present in the O3/P2 mixed-phase sodium-containing doped layered oxide material; nor a material with the general formula Na.sub.0.95Ni.sub.0.3167Mn.sub.0.3167Mg.sub.0.1583Ti.sub.0.2083O.sub.2 which comprises a mixture of phases in which a first phase has an O3-type structure and a second phase has a P2-type structure, wherein the amount of the first phase is 97% and the amount of the second phase is 3%, based on the combined total number of moles of the first and second phases in the O3/P2 mixed-phase sodium-containing doped layered oxide material.

2. An O3/P2 mixed-phase sodium-containing doped layered oxide material according to claim 1, selected from: NaNi.sub.0.400Mn.sub.0.490Mg.sub.0.100Ti.sub.0.010O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.95Ni.sub.0.3167Mn.sub.0.3167Mg.sub.0.1583Ti.sub.0.2083O.sub.2 (comprising 1% to 99%, but not 97%, of a first phase with an O3-type structure and 99% to 1%, but not 3%, of a second phase with a P2-type structure); Na.sub.0.925Ni.sub.0.4525Mn.sub.0.5275Mg.sub.0.01Ti.sub.0.01O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.867Ni.sub.0.383Mn.sub.0.467Mg.sub.0.05Ti.sub.0.1O.sub.2 (comprising 1% to 99 of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 (comprising 1% to 99%, but not 63%, of a first phase with an O3-type structure and 99% to 1%, but not 37%, of a second phase with a P2-type structure); Na.sub.0.8Ni.sub.0.35Mn.sub.0.48Mg.sub.0.05Ti.sub.0.12O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.77Ni.sub.0.28Mn.sub.0.31Mg.sub.0.05Ti.sub.0.25Fe.sub.0.11O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.77Ni.sub.0.225Mn.sub.0.115Mg.sub.0.01Ti.sub.0.35Fe.sub.0.3O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.833Ni.sub.0.317Mn.sub.0.417Mg.sub.0.05Ti.sub.0.117Co.sub.0.1O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.867Ni.sub.0.383Mn.sub.0.467Mg.sub.0.05Ti.sub.0.1O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.85Ni.sub.0.325Mn.sub.0.525Mg.sub.0.100Ti.sub.0.05O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.85Ni.sub.0.325Mn.sub.0.499Mg.sub.0.100Ti.sub.0.076O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.77Ni.sub.0.305Mn.sub.0.51Mg.sub.0.025Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure; Na.sub.0.77Ni.sub.0.305Mn.sub.0.535Mg.sub.0.025Ti.sub.0.025Al.sub.0.055Co.sub.0.055O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure; NaNi.sub.0.4Mn.sub.0.49Mg.sub.0.1Ti.sub.0.01O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.77Ni.sub.0.28Mn.sub.0.51Mg.sub.0.05Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.833Fe.sub.0.200Mn.sub.0.483Mg.sub.0.0917Cu.sub.0.225O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.775Ni.sub.0.35Mn.sub.0.475Ti.sub.0.1Al.sub.0.075O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); and Na.sub.0.833Ca.sub.0.05Ni.sub.0.3417Mn.sub.0.4417Mg.sub.0.125Ti.sub.0.0917O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Wherein the percentage values for each of the first and second phases are based on the combined total number of moles of the first and second phases present in the O3/P2 mixed phase sodium-containing doped layered oxide material.

3. A process of preparing an O3/P2 mixed-phase sodium-containing doped layered oxide material according to claim 1, comprising the steps: i) forming a mixture of precursor materials to provide metal atoms in the stoichiometric ratios that are present in the O3/P2 mixed-phase sodium-containing doped layered oxide material of the general formula; and ii) heating the resulting mixture of precursor materials at a temperature of at least 500° C. to yield the O3/P2 mixed-phase sodium-containing doped layered oxide material, wherein the process does not involve either: i) forming a mixture of precursor materials which provide metal atoms in the stoichiometric ratios that are present in an O3/P2 mixed-phase sodium-containing doped layered oxide material with the formula Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.100Ti.sub.0.117O.sub.2 and ii) heating the resulting mixture at 900° C. for 10 hours to produce a O3/P2 mixed-phase sodium-containing doped layered oxide material which comprises a mixture of phases in which a first phase has an O3-type structure and a second phase has a P2-type structure, wherein the amount of the first phase is 63% and the amount of the second phase is 37%, based on the combined total number of moles of the first and second phases present in the O3/P2 mixed-phase sodium-containing doped layered oxide material; or i) forming a mixture of precursor materials which provide metal atoms in the stoichiometric ratios that are present in an O3/P2 mixed-phase sodium-containing doped layered oxide material with the formula Na.sub.0.95Ni.sub.0.3167Mn.sub.0.3167Mg.sub.0.1583Ti.sub.0.2083O.sub.2 and ii) heating the resulting mixture at 900° C. for 4 minutes to produce a O3/P2 mixed-phase sodium-containing doped layered oxide material which comprises a mixture of phases in which a first phase has an O3-type structure and a second phase has a P2-type structure, wherein the amount of the first phase is 97% and the amount of the second phase is 3%, based on the combined total number of moles of the first and second phases present in the O3/P2 mixed-phase sodium-containing doped layered oxide material.

4. A process according to claim 3 for preparing O3:P2 mixed-phase sodium-containing doped layered oxide materials selected from: NaNi.sub.0.400Mn.sub.0.490Mg.sub.0.100Ti.sub.0.010O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.95Ni.sub.0.3167Mn.sub.0.3167Mg.sub.0.1583Ti.sub.0.2083O.sub.2 (comprising 1% to 99%, but not 97%, of a first phase with an O3-type structure and 99% to 1%, but not 3%, of a second phase with a P2-type structure); Na.sub.0.925Ni.sub.0.4525Mn.sub.0.5275Mg.sub.0.01Ti.sub.0.01O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.867Ni.sub.0.383Mn.sub.0.467Mg.sub.0.05Ti.sub.0.1O.sub.2 (comprising 1% to 99 of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 (comprising 1% to 99%, but not 63%, of a first phase with an O3-type structure and 99% to 1%, but not 37%, of a second phase with a P2-type structure); Na.sub.0.8Ni.sub.0.35Mn.sub.0.48Mg.sub.0.05Ti.sub.0.12O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.77Ni.sub.0.28Mn.sub.0.31Mg.sub.0.05Ti.sub.0.25Fe.sub.0.11O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.77Ni.sub.0.225Mn.sub.0.115Mg.sub.0.01Ti.sub.0.35Fe.sub.0.3O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.833Ni.sub.0.317Mn.sub.0.417Mg.sub.0.05Ti.sub.0.117Co.sub.0.1O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.867Ni.sub.0.383Mn.sub.0.467Mg.sub.0.05Ti.sub.0.1O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.85Ni.sub.0.325Mn.sub.0.525Mg.sub.0.100Ti.sub.0.05O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.85Ni.sub.0.325Mn.sub.0.499Mg.sub.0.100Ti.sub.0.076O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.77Ni.sub.0.305Mn.sub.0.51Mg.sub.0.025Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure; Na.sub.0.77Ni.sub.0.305Mn.sub.0.535Mg.sub.0.025Ti.sub.0.025Al.sub.0.055Co.sub.0.055O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure; NaNi.sub.0.4Mn.sub.0.49Mg.sub.0.1Ti.sub.0.01O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.77Ni.sub.0.28Mn.sub.0.51Mg.sub.0.05Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.833Fe.sub.0.200Mn.sub.0.483Mg.sub.0.0917Cn.sub.0.225O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); Na.sub.0.775Ni.sub.0.35Mn.sub.0.475Ti.sub.0.1Al.sub.0.075O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); and Na.sub.0.833Ca.sub.0.05Ni.sub.0.3417Mn.sub.0.4417Mg.sub.0.125Ti.sub.0.0917O.sub.2 (comprising 1% to 99% of a first phase with an O3-type structure and 99% to 1% of a second phase with a P2-type structure); wherein the percentage values for each of the first and second phases are based on the combined total number of moles of the first and second phases present in the O3/P2 mixed phase sodium-containing doped layered oxide material.

5. An energy storage device comprising one or more O3/P2 mixed-phase sodium-containing doped layered oxide materials according to claim 1.

6. An energy storage device according to claim 5 selected from a battery, a rechargeable battery, an electrochemical device and an electrochromic device.

7. An electrode comprising one or more O3/P2 mixed-phase sodium-containing doped layered oxide materials according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0201] The present invention will now be described with reference to the following figures in which:

[0202] FIG. 1 is the XRD profile of the known material NaNi.sub.0.5Mn.sub.0.5O.sub.2 (CE1);

[0203] FIG. 2 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//NaNi.sub.0.5Mn.sub.0.5O.sub.2 (CE1) cell;

[0204] FIG. 3 FIG. 3 shows the constant current cycling (CC/CV) of a full Na-ion cell comprising hard carbon and O3-NaNi0.5Mn0.5O2 (CE1), in the voltage range 1.0-4.3 V, at 30° C., in an electrolyte comprising 0.5 M NaPF6 dissolved in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC), with glass fibre filter paper (Whatman® Grade GF/A) used as a separator;

[0205] FIG. 4 is the XRD profile of the known material NaNi.sub.0.5Ti.sub.0.5O.sub.2 (CE2);

[0206] FIG. 5 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//NaNi.sub.0.5Ti.sub.0.5O.sub.2 (CE2) cell;

[0207] FIG. 6 shows the constant current cycling (CC/CV) of a full Na-ion cell comprising hard carbon and O3-NaNi.sub.0.5Ti.sub.0.5O.sub.2 (CE2), in the voltage range 1.0-4.3 V, at 30° C., in an electrolyte comprising 0.5 M NaPF.sub.6 dissolved in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC), with glass fibre filter paper (Whatman® Grade GF/A) used as a separator;

[0208] FIG. 7 is the XRD profile for the known compound P2-Na.sub.0.667Ni.sub.0.333Mn.sub.0.667O.sub.2 (CE3);

[0209] FIG. 8 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//Na.sub.0.667Ni.sub.0.333Mn.sub.0.667O.sub.2 (CE3) cell;

[0210] FIG. 9 shows the constant current cycling (CC/CV) of a full Na-ion cell comprising hard carbon and P2-Na.sub.0.667Ni.sub.0.333Mn.sub.0.667O.sub.2 (CE3), in the voltage range 1.0-4.3 V, at 30° C., in an electrolyte comprising 0.5 M NaPF.sub.6 dissolved in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC), with glass fibre filter paper (Whatman® Grade GF/A) used as a separator;

[0211] FIG. 10 is the XRD profile for O3/P2-Na.sub.0.667Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 prepared in Example 2;

[0212] FIG. 11 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O (Example 2) cell;

[0213] FIG. 12 shows the constant current cycling (CC/CV) of a full Na-ion cell comprising hard carbon and O3/P2-Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 (Example 2), in the voltage range 1.0-4.3 V, at 30° C., in an electrolyte comprising 0.5 M NaPF.sub.6 dissolved in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC), with glass fibre filter paper (Whatman® Grade GF/A) used as a separator;

[0214] FIG. 13 is the XRD profile for O3/P2-Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 prepared in Example 4;

[0215] FIG. 14 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 (Example 4) cell;

[0216] FIG. 15 shows the constant current cycling (CC/CV) of a full Na-ion cell comprising hard carbon and O3/P2-Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 (Example 4), in the voltage range 1.0-4.3 V, at 30° C., in an electrolyte comprising 0.5 M NaPF.sub.6 dissolved in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC), with glass fibre filter paper (Whatman® Grade GF/A) used as a separator;

[0217] FIG. 16 is the XRD profile for O3/P2-Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 prepared in Example 8;

[0218] FIG. 17 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 (Example 8) cell;

[0219] FIG. 18 shows the constant current cycling (CC/CV) of a full Na-ion cell comprising hard carbon and O3/P2-Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 (Example 8), in the voltage range 1.0-4.3 V, at 30° C., in an electrolyte comprising 0.5 M NaPF.sub.6 dissolved in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC), with glass fibre filter paper (Whatman® Grade GF/A) used as a separator;

[0220] FIG. 19 is a graph to show the relationship between reaction temperature and the amount of an O3-type phase relative to the amount of a P2-type phase when preparing Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2;

[0221] FIG. 20 is a graph to show the relationship between reaction temperature and the amount of an O3-type phase relative to the amount of a P2-type phase when preparing Na.sub.0.8Ni.sub.0.35Mn.sub.0.48Mg.sub.0.05Ti.sub.0.12O.sub.2; and

[0222] FIG. 21 is a graph to show the relationship between reaction temperature and the amount of an O3-type phase relative to the amount of a P2-type phase when preparing Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.100Ti.sub.0.117O.sub.2.

DETAILED DESCRIPTION

[0223] General Method for Making O3/P2 Mixed Phase Sodium-Containing Doped Layered Oxide Materials of the Present Invention: [0224] 1) Mix together the precursor materials to provide the metal atoms in the stoichiometric ratios that are present in a target O3/P2 mixed phase sodium-containing doped layered oxide material of the above described general formula, and press the resulting precursor mixture into a pellet; [0225] 2) Heat the resulting pelletized precursor mixture in a furnace under a suitable atmosphere comprising for example ambient air, nitrogen or an inert atmosphere (e.g. argon) (the gases may be flowing but need not be so, and may be pure or a mixture), over a ramp time of 0 to 20 hours, until the pelletized mixture reaches the desired reaction temperature (this will be a temperature of at least 500° C.). The ramp rate used will be the rate of heating (° C./min) needed to ensure that the reactants are uniformly heated to the required reaction temperature in a reasonable time. A person skilled in this art will know that this will depend on the efficiency of the heating equipment used, whether or not a continuous feed furnace/kiln is employed, whether the equipment and/or the reactants are preheated and the batch size. Typical ramp rates are 2° C. to 20° C. per minute. Continue heating for a reaction time of from 30 seconds up to 64 hours until the target O3/P2 mixed phase sodium-containing doped layered oxide material forms; and [0226] 3) cool, optionally grind the target material to a powder.

[0227] Table 1 below lists the precursor materials and heating conditions used to prepare the O3/P2 mixed phase sodium-containing doped layered oxide materials.

TABLE-US-00001 TABLE 1 Furnace Conditions (reaction temperature Example No. Starting (° C.), gas, O3/P2 (Sample No.) Composition Materials Reaction time) Content CE1 O3—NaNi.sub.0.5Mn.sub.0.5O.sub.2 0.5 Na.sub.2CO.sub.3, 900° C., air, 100% O3 (X2895) (comparative example) 0.5 NiCO.sub.3, 8 hours 0.5 MnO.sub.2 CE2 O3—NaNi.sub.0.5Ti.sub.0.5O.sub.2 0.5 Na.sub.2CO.sub.3, 900° C., air, 100% O3 (X2896) (comparative example) 0.5 NiCO.sub.3, 8 hours 0.5 TiO.sub.2 CE3 Na.sub.0.667Ni.sub.0.333Mn.sub.0.667O.sub.2 0.333 Na.sub.2CO.sub.3, 900° C., air, 100% P2 (X2748) (comparative example) 0.333 NiCO.sub.3, 8 hours 0.667 MnO.sub.2 Example 1 Na.sub.0.8Ni.sub.0.35Mn.sub.0.48Mg.sub.0.05Ti.sub.0.12O.sub.2 0.4 Na.sub.2CO.sub.3, 1100° C., air, 96% O3 (X2883) 1100° C. 0.35 NiCO.sub.3, 8 hours 4% P2 [Na] = 0.80 0.48 MnO.sub.2, 0.05 Mg(OH).sub.2, 0.12 TiO.sub.2 Ex. 2 Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 0.433 Na.sub.2CO.sub.3 850° C., air, 78% O3 (X2505) 0.333 NiCO.sub.3 8 hours 22% P2 [Na] = 0.867 0.467 MnO.sub.2 0.1 Mg(OH).sub.2 0.1 TiO.sub.2 Ex. 3 Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 0.433 Na.sub.2CO.sub.3 800° C., air, 51% O3 (X2504) 0.333 NiCO.sub.3 8 hours 49% P2 [Na] = 0.867 0.467 MnO.sub.2 0.1 Mg(OH).sub.2 0.1 TiO.sub.2 Ex. 4 Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1 Ti.sub.0.1O.sub.2 0.433 Na.sub.2CO.sub.3 900° C., air, 90% O3 (X2506) 0.333 NiCO.sub.3 8 hours 10% P2 [Na] = 0.867 0.467 MnO.sub.2 0.1 Mg(OH).sub.2 0.1 TiO.sub.2 Ex. 5 Na.sub.0.925Ni.sub.0.453Mn.sub.0.528Mg.sub.0.01Ti.sub.0.01O.sub.2 0.4625 Na.sub.2CO.sub.3 800° C., air, 73% O3 (X2835) 0.4525 NiCO.sub.3 64 hours 27% P2 [Na] = 0.925 0.5275 MnO.sub.2 0.01 Mg(OH).sub.2 0.01 TiO.sub.2 Ex. 6 Na.sub.0.925Ni.sub.0.453Mn.sub.0.528Mg.sub.0.01Ti.sub.0.01O.sub.2 0.4625 Na.sub.2CO.sub.3 900° C., air, 95% O3 (X2836) 0.4525 NiCO.sub.3 8 hours 5% P2 [Na] = 0.925 0.5275 MnO.sub.2 0.01 Mg(OH).sub.2 0.01 TiO.sub.2 Ex. 7 Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 0.4167 Na.sub.2CO.sub.3 900° C., air, 56% O3 (X2666) 0.3167 NiCO.sub.3 1 minute 44% P2 [Na] = 0.833 0.4667 MnO.sub.2 0.1 Mg(OH).sub.2 0.1167 TiO.sub.2 Ex. 8 Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 0.4167 Na.sub.2CO.sub.3 900° C., air, 68% O3 (X2663) 0.3167 NiCO.sub.3 30 minutes 32% P2 [Na] = 0.833 0.4667 MnO.sub.2 0.1 Mg(OH).sub.2 0.1167 TiO.sub.2 Ex. 9 Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 0.4167 Na.sub.2CO.sub.3 900° C., air, 71% O3 (X2799) 0.3167 NiCO.sub.3 8 hours 29% P2 [Na] = 0.833 0.4667 MnO.sub.2 0.1 Mg(OH).sub.2 0.1167 TiO.sub.2 Ex. 10 Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 0.4167 Na.sub.2CO.sub.3 900° C., air, 75% O3 (X2662) 0.3167 NiCO.sub.3 12 hours 25% P2 [Na] = 0.833 0.4667 MnO.sub.2 0.1 Mg(OH).sub.2 0.1167 TiO.sub.2 Ex. 11 Na.sub.0.833Ni.sub.0.317Mn.sub.0.417Mg.sub.0.05Ti.sub.0.117Co.sub.0.1O.sub.2 0.417 Na.sub.2CO.sub.3 900° C., air, 87% O3 (X2512) 0.317 NiCO.sub.3 8 hours 13% P2 0.467 MnO.sub.2 0.05 Mg(OH).sub.2 0.067 TiO.sub.2 0.1 CoCO.sub.3 Ex. 12 Na.sub.0.833Ni.sub.0.317Mn.sub.0.417Mg.sub.0.05Ti.sub.0.117Co.sub.0.1O.sub.2 0.417 Na.sub.2CO.sub.3 850° C., air, 67% O3 (X2519) 0.317 NiCO.sub.3 8 hours 33% P2 0.467 MnO.sub.2 0.05 Mg(OH).sub.2 0.067 TiO.sub.2 0.1 CoCO.sub.3 Ex. 13 Na.sub.0.833Ni.sub.0.317Mn.sub.0.417Mg.sub.0.05Ti.sub.0.117Co.sub.0.1O.sub.2 0.417 Na.sub.2CO.sub.3 800° C., air, 66% O3 (X2520) 0.317 NiCO.sub.3 8 hours 34% P2 0.467 MnO.sub.2 0.05 Mg(OH).sub.2 0.067 TiO.sub.2 0.1 CoCO.sub.3 Ex. 14 Na.sub.0.8Ni.sub.0.35Mn.sub.0.48Mg.sub.0.05Ti.sub.0.12O.sub.2 0.4 Na.sub.2CO.sub.3 1000° C., air, 67% O3 (X2878) 0.35 NiCO.sub.3 8 hours 33% P2 0.48 MnO.sub.2 0.05 Mg(OH).sub.2 0.12 TiO.sub.2 Ex. 15 Na.sub.0.77Ni.sub.0.28Mn.sub.0.31Mg.sub.0.05Ti.sub.0.25Fe.sub.0.11O.sub.2 0.385 Na.sub.2CO.sub.3 900° C., air, 76% O3, (X2888) 0.28 NiCO.sub.3 1 hour 24% P2 0.31 MnO.sub.2 0.05 Mg(OH).sub.2 0.25 TiO.sub.2 0.055 Fe.sub.2O.sub.3 Ex. 16 Na.sub.0.77Ni.sub.0.28Mn.sub.0.31Mg.sub.0.05Ti.sub.0.25Fe.sub.0.11O.sub.2 0.385 Na.sub.2CO.sub.3 900° C., air, 72% O3, (X2893) 0.28 NiCO.sub.3 8 hours 28% P2 0.31 MnO.sub.2 0.05 Mg(OH).sub.2 0.25 TiO.sub.2 0.055 Fe.sub.2O.sub.3 Ex. 17 Na.sub.0.85Ni.sub.0.325Mn.sub.0.499Mg.sub.0.100Ti.sub.0.076O.sub.2 0.425 Na.sub.2CO.sub.3 800° C., air, 65% O3, (X2890) 0.325 NiCO.sub.3 8 hours 35% P2 0.499 MnO.sub.2 0.1 Mg(OH).sub.2 0.076 TiO.sub.2 Ex. 18 Na.sub.0.85Ni.sub.0.325Mn.sub.0.525Mg.sub.0.100Ti.sub.0.05O.sub.2 0.425 Na.sub.2CO.sub.3 800° C., air, 77% O3, (X2891) 0.325 NiCO.sub.3 8 hours 23% P2 0.525 MnO.sub.2 0.1 Mg(OH).sub.2 0.05 TiO.sub.2 Ex. 19 Na.sub.0.77Ni.sub.0.305Mn.sub.0.51Mg.sub.0.025Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 0.385 Na.sub.2CO.sub.3 850° C., air, 11% O3, (X2717) 0.305 NiCO.sub.3 8 hours 89% P2 0.51 MnO.sub.2 0.025 Mg(OH).sub.2 0.05 TiO.sub.2 0.055Al(OH).sub.3 0.055CoCO.sub.3 Ex. 20 Na.sub.0.77Ni.sub.0.305Mn.sub.0.51Mg.sub.0.025Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 0.385 Na.sub.2CO.sub.3 850° C., air, 5% O3, (X2718) 0.305 NiCO.sub.3 8 hours 95% P2 0.51 MnO.sub.2 0.025 Mg(OH).sub.2 0.05 TiO.sub.2 0.055Al(OH).sub.3 0.055CoCO.sub.3 Ex. 21 NaNi.sub.0.400Mn.sub.0.490Mg.sub.0.1Ti.sub.0.01O.sub.2 0.5 Na.sub.2CO.sub.3 800° C., air, 44% O3, (X2892) 0.4 NiCO.sub.3 8 hours 56% P2 0.49 MnO.sub.2 0.1 Mg(OH).sub.2 0.01 TiO.sub.2 Ex. 22 Na.sub.0.77Ni.sub.0.28Mn0.51 Mg.sub.0.05Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 0.385 Na.sub.2CO.sub.3 850° C., air, 13% O3, X2712 0.28 NiCO.sub.3 8 hours 87% P2 0.51 MnO.sub.2 0.05 Mg(OH).sub.2 0.05 TiO.sub.2 0.055Al(OH).sub.3 0.055CoCO.sub.3 Ex. 23 Na.sub.0.77Ni.sub.0.28Mn.sub.0.51Mg.sub.0.05Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 0.385 Na.sub.2CO.sub.3 900° C., air, 14% O3, X2670 0.28 NiCO.sub.3 8 hours 86% P2 0.51 MnO.sub.2 0.05 Mg(OH).sub.2 0.05 TiO.sub.2 0.055 Al(OH).sub.3 0.055 CoCO3 Ex. 24 Na.sub.0.77Ni.sub.0.28Mn.sub.0.51Mg.sub.0.05Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 0.385 Na.sub.2CO.sub.3 950° C., air, 8 17% O3, X2900 0.28 NiCO.sub.3 hours 83% P2 0.51 MnO.sub.2 0.05 Mg(OH).sub.2 0.05 TiO.sub.2 0.055Al(OH).sub.3 0.055CoCO.sub.3 Ex. 25 Na.sub.0.77Ni.sub.0.28Mn.sub.0.51Mg.sub.0.05Ti.sub.0.05Al.sub.0.055Co.sub.0.055O.sub.2 0.385 Na.sub.2CO.sub.3 1000° C., air, 8 21% O3, X2901 0.28 NiCO.sub.3 hours 79% P2 0.51 MnO.sub.2 0.05 Mg(OH).sub.2 0.05 TiO.sub.2 0.055Al(OH).sub.3 0.055CoCO.sub.3 Ex. 26 Na.sub.0.833Fe.sub.0.200Mn.sub.0.483Mg.sub.0.0917Cu.sub.0.225O.sub.2 0.4167 Na.sub.2CO.sub.3, 700° C., air, 85% O3 (X2994) 0.1000 Fe.sub.2O.sub.3, 20 hours 15% P2 [Na] = 0.833 0.4333 MnO.sub.2, 0.0917 Mg(OH).sub.2, 0.2250 CuO Ex. 27 NaLi.sub.0.05Ni.sub.0.3Mn.sub.0.525Mg.sub.0.025Cu.sub.0.1O.sub.2 0.5 Na.sub.2CO.sub.3, 800° C., air, 54% O3 (X2987) 0.025 Li.sub.2CO.sub.3, 8 hours 46% P2 [Na] = 1 0.3 NiCO.sub.3, 0.525 MnO.sub.2, 0.025 Mg(OH).sub.2, 0.1 CuO Ex. 28 Na.sub.0.775Ni.sub.0.35Mn.sub.0.475Ti.sub.0.1Al.sub.0.075O.sub.2 0.3875 Na.sub.2CO.sub.3, 900° C., air, 24% O3 (X2645) 0.35 NiCO.sub.3, 8 hours 76% P2 [Na] = 0.775 0.475 MnO.sub.2, 0.1 TiO.sub.2, 0.075 Al(OH).sub.3 Ex. 29 Na.sub.0.833Ca.sub.0.05Ni.sub.0.3417Mn.sub.0.4417Mg.sub.0.125Ti.sub.0.0917O.sub.2 0.4167 Na.sub.2CO.sub.3, 900° C., air, 84% O3 (X2809) 0.05 CaCO.sub.3, 8 hours 16% P2 [Na] = 0.833 0.34167 NiCO.sub.3, 0.44167 MnO.sub.2, 0.125 Mg(OH).sub.2, 0.09167 TiO.sub.2

[0228] Product Analysis Using XRD

[0229] Analysis by X-ray diffraction techniques was conducted using a Siemens® D5000 powder diffractometer to confirm that the desired target compositions had been prepared, to establish the phase purity of the product material and to determine the types of impurities present. From this information it is possible to determine the lattice parameters of the unit cells and the relative phase ratios.

[0230] The general XRD operating conditions used to analyse the materials are as follows:

[0231] Slits sizes: 1 mm, 1 mm, 0.1 mm

[0232] Range: 2θ=5°-60°

[0233] X-ray Wavelength=1.5418 Å (Angstroms) (Cu Kα)

[0234] Speed: 1.0 seconds/step

[0235] Increment: 0.025°

[0236] Electrochemical Results

[0237] The target compositions were tested using a Na-ion test cell using a hard carbon anode. Cells may be made using the following procedures:

[0238] A Na-ion electrochemical test cell containing the active material is constructed as follows:

[0239] Generic Procedure to Make a Hard Carbon Na-Ion Cell

[0240] The positive electrode is prepared by solvent-casting a slurry of the active material, conductive carbon, binder and solvent. The conductive carbon used is Super C65C65 (Timcal®). PVdF is used as the binder, and N-methyl-2-pyrrolidone (NMP) is employed as the solvent. The slurry is then cast onto aluminium foil and heated until most of the solvent evaporates and an electrode film is formed. The electrode is then dried under dynamic vacuum at about 120° C. The electrode film contains the following components, expressed in percent by weight: 89% active material (doped layered oxide composition), 6% Super C65 carbon, and 5% PVdF binder.

[0241] The negative electrode is prepared by solvent-casting a slurry of the hard carbon active material (Carbotron® P/J, supplied by Kureha), conductive carbon, binder and solvent. The conductive carbon used is Super C65 (Timcal®). PVdF is used as the binder, and N-Methyl-2-pyrrolidone (NMP) is employed as the solvent. The slurry is then cast onto aluminium foil and heated until most of the solvent evaporates and an electrode film is formed. The electrode is then dried further under dynamic vacuum at about 120° C. The electrode film contains the following components, expressed in percent by weight: 88% active material, 3% Super C65 carbon, and 9% PVdF binder.

[0242] Cell Testing

[0243] The cells are tested as follows, using Constant Current Cycling techniques.

[0244] The cell is cycled at a given current density between pre-set voltage limits. A commercial battery cycler from Maccor Inc. (Tulsa, Okla., USA) is used. On charge, alkali ions are extracted from the cathode active material. During discharge, alkali ions are re-inserted into the cathode active material.

[0245] A summary of the test results is given below in Table 2:

TABLE-US-00002 TABLE 2 D1 D1 Specific Average Capacity Cell Discharge Discharge Discharge on Cell Discharge Capacity Energy Energy Example No. Discharge Voltage Fade Fade Fade (Sample No.) Cell# [mAh/g] [V] [%/cycle] [%] [%/cycle] CE1 803039 141 3.08 3.15 31 (9 cycles) 3.4 (X2895) CE2 803040 107 2.75 2.66 59 (19 cycles) 3.0 (X2896) CE3 802064 127 3.39 1.35 62 (38 cycles) 1.6 (X2748) Example 1 802066 118 3.28 0.08 8.5 (30 cycles) 0.3 (X2883) [Na] = 0.80 Example 2 608010 144 3.09 0.04 5.9 (36 cycles) 0.2 (X2505) [Na] = 0.867 Example 3 608016 137 3.06 0.13 9.4 (35 cycles) 0.3 (X2504) [Na] = 0.867 Example 4 608011 143 3.09 0.07 9 (30 cycles) 0.3 (X2506) [Na] = 0.867 Example 5 802050 152 3.2 0.64 27 (29 cycles) 0.9 (X2835) [Na] = 0.925 Example 6 802010 155 3.05 0.60 28 (30 cycles) 0.9 (X2836) [Na] = 0.925 Example 7 706007 127 3.11 0.89 27.7 (30 cycles) 0.9 (X2666) [Na] = 0.833 Example 8 706006 132 3.10 0.07 9.5 (32 cycles) 0.3 (X2663) [Na] = 0.833 Example 9 801017 132 3.09 0.08 17.6 (80 cycles) 0.2 (X2799) [Na] = 0.833 Example 10 706005 124 3.11 0.21 18 (39 cycles) 0.5 (X2662) [Na] = 0.833 Example 11 608029 133 3.15 0.11 12.5 (50 cycles) 0.2 (X2512) Example 12 608041 127 3.11 0.37 15.3 (30 cycles) 0.5 (X2519) Example 13 608042 137 3.11 0.07 6.3 (30 cycles) 0.2 (X2520) Example 15 803029 122 2.99 0.33 22 (40 cycles) 0.6 (X2888) Example 17 803031 131 3.09 1.35 22 (17 cycles) 1.0 X2890 Example 18 803032 132 3.10 0.05 3 (14 cycles) 0.2 X2891 Example 19 709040 120 3.23 0.17 15 (50 cycles) 0.3 X2717 Example 20 709041 118 3.21 0.17 14.5 (50 cycles) 0.3 X2718 Example 21 803037 126 3.04 0.49 13.8 (18 cycles) 0.8 X2892 Example 22 709025 119 3.19 0.02 6.1 (50 cycles) 0.1 X2712 Example 23 708018 125 3.23 0.06 9.2 (51 cycles) 0.2 X2670 Example 24 803052 112 3.23 0.09 0.5 (18 cycles) 0.0 X2900 Example 25 803053 109 3.32 0.05 0.02 (20 cycles) 0.0 X2901 Example 26 811026 76 2.65 0.02 13.6 (61 cycles) 0.2 (X2994) [Na] = 0.833 Example 27 811032 127 2.93 0.00 5.1 (39 cycles) 0.1 (X2987) [Na] = 1 Example 28 705040 124 3.29 0.29 27.4 (70 cycles) 0.4 (X2645) [Na] = 0.775 Example 29 801035 135 3.01 0.12 24.4 (100 cycles) 0.2 (X2809) [Na] = 0.833

[0246] Discussion of the Results

Comparative Example 1

[0247] NaNi.sub.0.5Mn.sub.0.5O.sub.2 (Sample X2895)

[0248] FIG. 1 shows the X-ray diffraction pattern of the known material NaNi.sub.0.5Mn.sub.0.5O.sub.2 (sample number X2895). The pattern shows that this material conforms to a single phase doped layered O3-type structure.

[0249] The data shown in FIGS. 2 and 3 are derived from the constant current cycling data for an O3-NaNi.sub.0.5Mn.sub.0.5O.sub.2 cathode active material in a Na-ion cell (cell #803039) where this cathode material was coupled with a hard carbon anode material. The electrolyte used was a solution of 0.5 M NaPF.sub.6 in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC). The constant current data were collected at an approximate current density of 0.25 mA/cm.sup.2 between voltage limits of 1.00 and 4.3 V. To ensure that the Na-ion cell was fully charged, the cell was potentiostatically held at 4.3 V at the end of the constant current charging process until the current density dropped to 10% of the constant current value. The testing was carried out at 30° C. During the charging process, sodium ions are extracted from the cathode active material, and inserted into the hard carbon anode. During the subsequent discharge process, sodium ions are extracted from the hard carbon and reinserted into the cathode active material.

[0250] FIG. 2 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//NaNi.sub.0.5Mn.sub.0.5O.sub.2 cell. These data demonstrate a relatively poor level of capacity retention and a relatively large level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes), indicating the relatively poor kinetic reversibility of the Na-ion extraction-insertion reactions in this cathode material.

[0251] FIG. 3 shows the constant current cycle life profile, i.e. the relationship between cathode specific capacity for discharge [mAh/g]) and cycle number for the hard carbon//NaNi.sub.0.5Mn.sub.0.5O.sub.2 cell. For cycle 1, the discharge specific capacity for the cathode is about 141 mAh/g. For cycle 9, the discharge specific capacity for the cathode is about 101 mAh/g. This represents a capacity fade of 28.37% over 9 cycles or an average of 3.15% per cycle. The cathode material under test clearly demonstrates relatively poor capacity retention behaviour.

Comparative Example 2

[0252] NaNi.sub.0.5Ti.sub.0.5O.sub.2 (Sample) X2896

[0253] The XRD pattern shown in FIG. 4 confirms that this material conforms to a single phase doped layered O3-type structure;

[0254] The data shown in FIGS. 5 and 6 are derived from the constant current cycling data for an O3-NaNi.sub.0.5Ti.sub.0.5O.sub.2 cathode active material in a Na-ion cell (cell #803040RH) where this cathode material was coupled with a hard carbon anode material. The electrolyte used was a solution of 0.5 M NaPF.sub.6 in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC). The constant current data were collected at an approximate current density of 0.25 mA/cm.sup.2 between voltage limits of 1.00 and 4.3 V. To ensure that the Na-ion cell was fully charged, the cell was potentiostatically held at 4.3 V at the end of the constant current charging process until the current density dropped to 10% of the constant current value. The testing was carried out at 30° C.

[0255] During the charging process, sodium ions are extracted from the cathode active material, and inserted into the hard carbon anode. During the subsequent discharge process, sodium ions are extracted from the hard carbon and reinserted into the cathode active material. FIG. 5 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//NaNi.sub.0.5Ti.sub.0.5O.sub.2 cell. These data demonstrate a relatively poor level of capacity retention and a relatively large level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes), indicating the relatively poor kinetic reversibility of the Na-ion extraction-insertion reactions in this cathode material.

[0256] FIG. 6 shows the constant current cycle life profile, i.e. the relationship between cathode specific capacity for discharge [mAh/g]) and cycle number for the hard carbon//NaNi.sub.0.5Ti.sub.0.5O.sub.2 cell. For cycle 1, the discharge specific capacity for the cathode is about 107 mAh/g. For cycle 19, the discharge specific capacity for the cathode is about 53 mAh/g. This represents a capacity fade of 50.47% over 19 cycles or an average of 2.66% per cycle. The cathode material under test clearly demonstrates relatively poor capacity retention behaviour.

Comparative Example 3

[0257] Na.sub.0.667Ni.sub.0.333Mn.sub.0.667O.sub.2 (Sample X2748)

[0258] FIG. 7 shows the X-ray diffraction pattern of the known material Na.sub.0.667Ni.sub.0.333Mn.sub.0.667O.sub.2 (sample number X2748). The pattern shows that this material conforms to a layered P2-type structure.

[0259] The data shown in FIGS. 8 and 9 are derived from the constant current cycling data for a P2-Na.sub.0.667Ni.sub.0.333Mn.sub.0.667O.sub.2 cathode active material in a Na-ion cell (cell #802064) where this cathode material was coupled with a hard carbon anode material. The electrolyte used was a solution of 0.5 M NaPF.sub.6 in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC). The constant current data were collected at an approximate current density of 0.25 mA/cm.sup.2 between voltage limits of 1.00 and 4.3 V. To ensure that the Na-ion cell was fully charged, the cell was potentiostatically held at 4.3 V at the end of the constant current charging process until the current density dropped to 10% of the constant current value. The testing was carried out at 30° C.

[0260] During the charging process, sodium ions are extracted from the cathode active material, and inserted into the hard carbon anode. During the subsequent discharge process, sodium ions are extracted from the hard carbon and reinserted into the cathode active material. FIG. 8 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//Na.sub.0.667Ni.sub.0.333Mn.sub.0.667O.sub.2 cell. These data demonstrate a relatively poor level of capacity retention and a relatively large level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes), indicating the relatively poor kinetic reversibility of the Na-ion extraction-insertion reactions in this cathode material.

[0261] FIG. 9 shows the constant current cycle life profile, i.e. the relationship between cathode specific capacity for discharge [mAh/g]) and cycle number for the hard carbon Na.sub.0.667Ni.sub.0.333Mn.sub.0.667O.sub.2 cell. For cycle 1, the discharge specific capacity for the cathode is about 127 mAh/g. For cycle 38, the discharge specific capacity for the cathode is about 62 mAh/g. This represents a capacity fade of 51.18% over 38 cycles or an average of 1.35% per cycle. The cathode material under test clearly demonstrates relatively poor capacity retention behaviour.

[0262] Results for a Selection of Representative Examples According to the Present Invention

Example 2

[0263] Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 (Sample X2505)

[0264] FIG. 10 shows the X-ray diffraction pattern of the material Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 (sample number X2505). The pattern shows that this material comprises a mixture of phases with a first phase with an O3-type structure and a second phase with a P2-type structure. The percentage amounts of the first and second phases were determined using Rietveld refinement.

[0265] The data shown in FIGS. 11 and 12 are derived from the constant current cycling data for an O3/P2-Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 cathode active material in a Na-ion cell (cell #608010 where this cathode material was coupled with a hard carbon anode material. The electrolyte used was a solution of 0.5 M NaPF.sub.6 in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC). The constant current data were collected at an approximate current density of 0.25 mA/cm.sup.2 between voltage limits of 1.00 and 4.3 V. To ensure that the Na-ion cell was fully charged, the cell was potentiostatically held at 4.3 V at the end of the constant current charging process until the current density dropped to 10% of the constant current value. The testing was carried out at 30° C.

[0266] During the charging process, sodium ions are extracted from the cathode active material, and inserted into the hard carbon anode. During the subsequent discharge process, sodium ions are extracted from the hard carbon and reinserted into the cathode active material. FIG. 11 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 cell. These data demonstrate an excellent level of capacity retention and a small level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes), indicating the excellent kinetic reversibility of the Na-ion extraction-insertion reactions. In addition, the generally symmetrical nature of the charge/discharge voltage profile confirms the excellent reversibility of the extraction-insertion reactions.

[0267] FIG. 12 shows the constant current cycle life profile, i.e. the relationship between cathode specific capacity for discharge [mAh/g]) and cycle number for the hard carbon//Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 cell. For cycle 1, the discharge specific capacity for the cathode is about 144 mAh/g. For cycle 36, the discharge specific capacity for the cathode is about 142 mAh/g. This represents a capacity fade of 1.39% over 36 cycles or an average of 0.04% per cycle. The cathode material under test clearly demonstrates excellent capacity retention behaviour.

Example 4

[0268] Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 (Sample X2506)

[0269] FIG. 13 shows the X-ray diffraction pattern of the material Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 (sample number X2506). The pattern shows that this material comprises a mixture of phases with a first phase with an O3-type structure and a second phase with a P2-type structure. The percentage amounts of the first and second phases were determined using Rietveld refinement.

[0270] The data shown in FIGS. 14 and 15 are derived from the constant current cycling data for an O3/P2-Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 cathode active material in a Na-ion cell (cell #608011) where this cathode material was coupled with a hard carbon anode material. The electrolyte used was a solution of 0.5 M NaPF.sub.6 in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC). The constant current data were collected at an approximate current density of 0.25 mA/cm.sup.2 between voltage limits of 1.00 and 4.3 V. To ensure that the Na-ion cell was fully charged, the cell was potentiostatically held at 4.3 V at the end of the constant current charging process until the current density dropped to 10% of the constant current value. The testing was carried out at 30° C.

[0271] During the charging process, sodium ions are extracted from the cathode active material, and inserted into the hard carbon anode. During the subsequent discharge process, sodium ions are extracted from the hard carbon and reinserted into the cathode active material. FIG. 14 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 cell. These data demonstrate an excellent level of capacity retention and a small level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes), indicating the excellent kinetic reversibility of the Na-ion extraction-insertion reactions. In addition, the generally symmetrical nature of the charge/discharge voltage profile confirms the excellent reversibility of the extraction-insertion reactions.

[0272] FIG. 15 shows the constant current cycle life profile, i.e. the relationship between cathode specific capacity for discharge [mAh/g]) and cycle number for the hard carbon//Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 cell. For cycle 1, the discharge specific capacity for the cathode is about 143 mAh/g. For cycle 30, the discharge specific capacity for the cathode is about 140 mAh/g. This represents a capacity fade of 2.10% over 30 cycles or an average of 0.07% per cycle. The cathode material under test clearly demonstrates excellent capacity retention behaviour.

Example 8

[0273] Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 (Sample X2663)

[0274] FIG. 16 shows the X-ray diffraction pattern of the material Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 (sample number X2663). The pattern shows that this material comprises a mixture of phases with a first phase with an O3-type structure and a second phase with a P2-type structure. The percentage amounts of the first and second phases were determined from these structural data.

[0275] The data shown in FIGS. 17 and 18 are derived from the constant current cycling data for an O3/P2-Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 cathode active material in a Na-ion cell (cell #706006) where this cathode material was coupled with a hard carbon anode material. The electrolyte used was a solution of 0.5 M NaPF.sub.6 in a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC). The constant current data were collected at an approximate current density of 0.25 mA/cm.sup.2 between voltage limits of 1.00 and 4.3 V. To ensure that the Na-ion cell was fully charged, the cell was potentiostatically held at 4.3 V at the end of the constant current charging process until the current density dropped to 10% of the constant current value. The testing was carried out at 30° C.

[0276] During the charging process, sodium ions are extracted from the cathode active material, and inserted into the hard carbon anode. During the subsequent discharge process, sodium ions are extracted from the hard carbon and reinserted into the cathode active material. FIG. 17 shows the cell voltage profile (i.e. Na-ion cell voltage [V] versus cumulative cathode specific capacity [mAh/g]) for the first 4 charge/discharge cycles of the hard carbon//Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 cell. These data demonstrate an excellent level of capacity retention and a small level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes), indicating the excellent kinetic reversibility of the Na-ion extraction-insertion reactions. In addition, the generally symmetrical nature of the charge/discharge voltage profile confirms the excellent reversibility of the extraction-insertion reactions.

[0277] FIG. 18 shows the constant current cycle life profile, i.e. the relationship between cathode specific capacity for discharge [mAh/g]) and cycle number for the hard carbon//Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.1Ti.sub.0.117O.sub.2 cell. For cycle 1, the discharge specific capacity for the cathode is about 132 mAh/g. For cycle 32, the discharge specific capacity for the cathode is about 129 mAh/g. This represents a capacity fade of 2.27% over 32 cycles or an average of 0.07% per cycle. The cathode material under test clearly demonstrates excellent capacity retention behaviour.

[0278] The Relationship Between Reaction Temperature and the Amount of an O3-Type Phase Produced, Relative to the Amount of a P2-Type Phase Produced.

[0279] Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2

TABLE-US-00003 TABLE 3 Synthesis Temper- O3 Target ature Content Stoichiometry Sample (° C.) (Mole %) Na.sub.0.867Ni.sub.0.333Mn.sub.0.467Mg.sub.0.1Ti.sub.0.1O.sub.2 X2504 800 51 X2505 850 78 X2506 900 90

[0280] Table 3 above and FIG. 19 show that as the synthesis temperature increases, the proportion of the phase that has an O3 structure increases relative to that of a phase with a P2 structure.

[0281] Na.sub.0.8Ni.sub.0.35Mn.sub.0.48Mg.sub.0.05Ti.sub.0.12O.sub.2

TABLE-US-00004 TABLE 4 Synthesis Temper- O3 Target ature Content Stoichiometry Sample (° C.) (Mole %) Na.sub.0.8Ni.sub.0.35Mn.sub.0.48Mg.sub.0.05Ti.sub.0.12O.sub.2 X2875 900 42 X2878 1000 67 X2883 1100 96

[0282] Table 4 above and FIG. 20 show that as the synthesis temperature increases, the proportion of the phase that has an O3 structure increases relative to that of a phase with a P2 structure.

[0283] Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.100Ti.sub.0.117O.sub.2

TABLE-US-00005 TABLE 5 Synthesis Temper- O3 Target ature Content Stoichiometry Sample (° C.) (Mole %) Na.sub.0.833Ni.sub.0.317Mn.sub.0.467Mg.sub.0.100Ti.sub.0.117O.sub.2 X2869 850 59 X2799 900 72

[0284] Table 5 above and FIG. 21 show that as the synthesis temperature increases, the proportion of the phase that has an O3 structure increases relative to that of a phase with a P2 structure.