An 03/P2 mixed-phase sodium-containing doped layered oxide material which comprises a mixture of phases, wherein a first phase has one or more 03-type structures and a second phase has one or more P2-type structures; further wherein the 03/P2 mixed-phase sodium-containing doped layered oxide material has the general formula: Na a A b M 1 c M 2 d M 3 e M 4 f M 5 g O 2±δ; wherein: A is an alkali metal selected from at least one of lithium and potassium; M 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 2 is one or more metals with an average oxidation state of 4+ selected from manganese, titanium and zirconium; M 3 is one or more metals with an average oxidation state of 2+ selected from magnesium, calcium, copper, zinc and cobalt; M 4 is one or more metals with an average oxidation state of 4+ selected from manganese, titanium and zirconium; and M 5 is one or more metals with an average oxidation state of 3+ selected from aluminium, 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 03/P2 mixed-phase sodium-containing doped layered oxide material is neither a material with the general formula Na 0.833 Ni 0.317 Mn 0.467 Mg 0.100 Ti 0.117 O 2 which comprises a mixture of phases in which a first phase has an 03-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 03/P2 mixed-phase sodium-containing doped layered oxide material; nor a material with the general formula Na 0.95 Ni 0.3167 Mn 0.3167 Mg 0.1583 Ti 0.2083 O 2 which comprises a mixture of phases in which a first phase has an 03-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 03/P2 mixed-phase sodium-containing doped layered oxide material. A is an alkali metal selected from at least one of lithium and potassium; M 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 2 is one or more metals with an average oxidation state of 4+ selected from manganese, titanium and zirconium; M 3 is one or more metals with an average oxidation state of 2+ selected from magnesium, calcium, copper, zinc and cobalt; M 4 is one or more metals with an average oxidation state of 4+ selected from manganese, titanium and zirconium; and M 5 is one or more metals with an average oxidation state of 3+ selected from aluminium, iron, cobalt, molybdenum, chromium, vanadium, scandium and yttrium; 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 03/P2 mixed-phase sodium-containing doped layered oxide material is neither a material with the general formula Na 0.833 Ni 0.317 Mn 0.467 Mg 0.100 Ti 0.117 O 2 which comprises a mixture of phases in which a first phase has an 03-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 03/P2 mixed-phase sodium-containing doped layered oxide material; nor a material with the general formula Na 0.95 Ni 0.3167 Mn 0.3167 Mg 0.1583 Ti 0.2083 O 2 which comprises a mixture of phases in which a first phase has an 03-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 03/P2 mixed-phase sodium-containing doped layered oxide material.