Lithium-ion batteries are of great interest for automotive applications but are expensive. Sodium is much more abundant and hence cheaper so for e.g. storing energy from renewables the higher mass of Na is no penalty. As a result Na-ion batteries are a hot topic. The challenge is to find Na insertion hosts as electrodes. Spinels have received little attention as positive electrodes. We have inserted Na in spinel Ni0.5Mn1.5O4 with promising capacity and high voltage. Capacity loss between 1st and 2nd discharges occurs as a result of transition metal migration into 8a sites. The large contrast with neutrons between Mn and Ni should resolve this. Layered Na0.67MnO2 exhibits excellent performance but shows many phase transitions. Substitution of Mg removes these transitions. We wish to make use of Polaris/GEM ability to obtain reliable occupancies to investigate this change in behaviour.