Layered sodium transition metal oxides, NaMO2 (M = Fe, Co etc.), are a promising class of cathode materials for applications in sodium ion These materials exhibits complex but interesting structural polymorphism, which we seek to investigate. By understanding this the e.g. stability and reversibility of these cathode materials can be improved to a great extent. We aim to study how atomic vibrations and bonding in these materials depend on (1) the nature of the transition metal, (2) the sodium content and (3) which polymorph is present. To do this, different configurations of two simple and well known cathode materials, namely NaFeO2 and NaCoO2 will be investigated by inelastic neutron scattering.