NaxFe1/2Mn1/2O2 has been identified as a potential cathode material for Na-ion batteries since it has comparable electrochemical performance to commercially available Li-ion cathodes and it is composed entirely of abundant elements. For x = 1 it has the same crystal structure as O3-LixCoO2, whereas for x = 2/3 it has the P2-NaxCoO2 structure. In both cases the planes of Na ions are sandwiched between O planes, but the difference in the stacking sequence of hexagonal planes leads to very different diffusion mechanisms. We propose to study the diffusion mechanism in two large powder samples of these compounds using quasi-elastic neutron scattering, taking advantage of the low instrumental background and repetition-rate multiplication on LET.