A sodium transition metal cathode material for a rechargeable sodium battery having a P2 layered bronze crystal structure, comprising at least 55 mol% manganese, wherein the manganese valence state is at least 3.75. The material undergoes a structural transformation to a secondary cathode material by extraction of sodium during the 1st charge of a rechargeable sodium battery comprising the sodium cathode material. The material has either a composition NaxM02 where M = Mn1-y-zLiyAz where z<0.2 and y<0.33 and 0.66