Sodium transition metal oxide compounds for Na-ion batteries

摘要

A composition comprises the general formula: X_w M¹_x Z_y M²_z2 Mⁱ_zi O_2±d, in which: X is sodium in +1 oxidation state or a mixture of group 1 metals in +1 oxidation state comprising sodium as a major constituent, and 0 w; M¹ is a transition metal in a +2 oxidation state and 0.05 ≦ x ≦ 0.5; Z is a group 1 element, or a mixture of group 1 elements, but excluding Li as the sole constituent, and 0.01≦ y ≦0.5; M² is a transition metal in a +4 oxidation state, a lanthanide in a +4 oxidation state, an actinide in a +4 oxidation state, or a mixture thereof, and z₂ 0; Mⁱ for i = 3, 4...n, is a transition metal, a lanthanide, an actinide, an alkaline earth metal, aluminium, gallium, indium, thallium, germanium, lead, antimony or bismuth, or a mixture thereof, and z_i ≧ 0 for each i = 3, 4...n; and d ≦ 0.2. It has been found that such materials may be charged to a capacity that is greater than the theoretical charging capacity of the material, as determined from the content of redox active elements in the material.