Doped nickelate compounds

1. A compound of the formula:

A 1-δ M 1 V M 2 W M 3 X M 4 Y M 5 Z O 2

wherein

A is one or more alkali metals comprising sodium and/or potassium, either alone or in a mixture with lithium as a minor constituent;

M 1 is nickel in oxidation state +2

M 2 comprises a metal in oxidation state +4 selected from one or more of manganese, titanium and zirconium;

M 3 comprises a metal in oxidation state +2, selected from one or more of magnesium, calcium, copper, zinc and cobalt;

M 4 comprises a metal in oxidation state +4, selected from one or more of titanium, manganese and zirconium;

M 5 comprises a metal in oxidation state +3, selected from one or more of aluminum, iron, cobalt, molybdenum, chromium, vanadium, scandium and yttrium;

wherein

0≦δ≦0.1

V is in the range 0<V<0.5;

W is in the range 0<W≦0.5;

X is in the range 0<X<0.5;

Y is in the range 0≦Y<0.5;

Z is ≧0;

and further wherein V+W+X+Y+Z=1.

2. A compound according to claim 1 wherein V is in the range 0.1≦V≦0.45; W is in the range 0<W≦0.5; X is in the range 0≦X<0.5; Y is in the range 0≦Y<0.5; Z is ≧0; and wherein V+W+X+Y+Z=1.

3. A compound according to claim 1 wherein V is in the range 0.3≦V≦0.45; W is in the range 0.1≦W≦0.5; X is in the range 0.05≦X<0.45; Y is in the range 0≦Y≦0.45; Z is ≧0; and wherein V+W+X+Y+Z=1.

4. A compound according to claim 1 wherein M 2 M 4 .

5. A compound according to claim 1 of the formula: NaNi 0.5−x Mn 0.5−x Mg x Ti x O 2 ; NaNi 0.5−x Mn 0.5−x Mg x/2 Ti x/2 Al x O 2 ; NaNi 0.5−x Mn 0.5−x Ca x Ti x O 2 ; NaNi 0.5−x Mn 0.5−x Co x Ti x O 2 ; NaNi 0.5−x Mn 0.5−x Cu x Ti x O 2 ; NaNi 0.5−x Mn 0.5−x Zn x Ti x O 2 ; NaNi 0.5−x Mn 0.5−x Mg x Zr x O 2 ; NaNi 0.5−x Mn 0.25−x/2 Ca x Ti 0.25+x/2 O 2 ; NaNi 0.5−x Mn 0.5 Ca x O 2 ; NaNi 0.5−x Mn 0.5−Y Ca x Ti Y O 2 ; NaNi 0.5−x Ti 0.5−x Mg x Mn x O 2 ; NaNi 0.5−x Ti 0.5−x Ca x Mn x O 2 ; NaNi 0.5−x Ti 0.5−x Cu x Mn x O 2 ; NaNi 0.5−x Ti 0.5−x Co x Mn x O 2 ; NaNi 0.5−x Ti 0.5−x Zn x Mn x O 2 ; NaNi 0.5−x Mn 0.5 Mg x O 2 ; NaNi 0.5−x Mn 0.5 Ca x O 2 ; NaNi 0.5−x Mn 0.5 Cu x O 2 , NaNi 0.5−x Mn 0.5 Co x O 2 ; NaNi 0.5−x Mn 0.5 Zn x O 2 ; NaNi 0.5−x Mn 0.5−y Mg x Ti y O 2 ; NaNi 0.5−x Mn 0.5−y Ca x Ti y O 2 ; NaNi 0.5−x Mn 0.5−y Cu x Ti y O 2 ; NaNi 0.5−x Mn 0.5−y CO x Ti y O 2 ; NaNi 0.5−x Mn 0.5−y Zn x Ti y O 2 ; NaNi 0.5−x Mn 0.25−x/2 Mg x Ti 0.25+x/2 O 2 ; NaNi 0.5−x Mn 0.25−x/2 Ca x Ti 0.25+x/2 O 2 ; NaNi 0.5−x Mn 0.25−x/2 Cu x Ti 0.25+x/2 O 2 ; NaNi 0.5−x Mn 0.25−x/2 CO x Ti 0.25+x/2 O 2 ; NaNi 0.5−x Mn 0.25−x/2 Zn x Ti 0.25+x/2 O 2 ; NaNi 0.5−x Mn 0.5−x Mg x/2 Ti x/2 Al x O 2 ; NaNi 0.5−x Mn 0.5−x Ca x/2 Ti x/2 Al x O 2 ; NaNi 0.5−x Mn 0.5−x Cu x/2 Ti x/2 Al x O 2 ; NaNi 0.5−x Mn 0.5−x Co x/2 Ti x/2 Al x O 2 ; NaNi 0.5−x Mn 0.5−x Zn x/2 Ti x/2 Al x O 2 and Na 0.95 N 0.3167 Ti 0.3167 Mg 0.1583 Mn 0.2083 O 2 .

6. An electrode comprising an active compound according to claim 1 .

7. An electrode according to claim 6 used in conjunction with a counter electrode and one or more electrolyte materials.

8. An electrode according to claim 7 wherein the electrolyte material comprises an aqueous electrolyte material.

9. An electrode according to claim 7 wherein the electrolyte material comprises a non-aqueous electrolyte.

10. An energy storage device comprising an electrode according to claim 6 .

11. An energy storage device according to claim 10 suitable for use as one or more of the following: a sodium and/or potassium ion cell; a sodium and/or potassium metal cell; a non-aqueous electrolyte sodium and/or potassium ion cell; and an aqueous electrolyte sodium and/or potassium ion cell.

12. A rechargeable battery comprising an electrode according to claim 6 .

13. An electrochemical device comprising an electrode according to claim 6 .

14. An electrochromic device comprising an electrode according to claim 6 .

15. A method of preparing the compounds according to claim 1 comprising the steps of:

a) mixing starting materials together,

b) heating the mixed starting materials in a furnace at a temperature of between 400° C. and 1500° C., for between 2 and 20 hours to give a reaction product; and

c) allowing the reaction product to cool.