There is great interest in scaling up Li-ion batteries for use in electric vehicles, requiring cheap and safe cathodes. It has been demonstrated that when extra Li is added to layered LiMO2 electrodes, notably those in which M = Mn & Ni, or Mn, Ni & Co, capacities > 200 mAh/g can be obtained if the electrodes are charged to > 4.5 V. We have demonstrated in a combined neutron-diffraction/DEMS study that, when charged to 4.6 V, the Li2MnO3 component is electrochemically activated by the removal of lithium and oxygen (a net Li2O loss). There are further subtle structural changes observed on extended cycling, revealed by the evolution of the charge-discharge curves. It is these hitherto uncharacterized changes that we wish to study in this epxeriment. We propose to gain additional insights into the structure by investigating materials prepared using a range of Ni isotope ratios.