Thermodynamic stability, Na-ion mobility and oxygen deficiency in Na0.7MnO2 P2-type phase

The overwhelming majority of mobile applications, ranging from portable consumer electronics to electric cars, currently rely on lithium-ion battery technology. Whilst lithium-based power storage has advantages in terms of high voltage and high gravimetric capacities, there are a number of disadvantages. Sodium-ion batteries have received extensive interest, largely due to the high earth abundance of Na, and are particularly attractive for static energy storage applications for load-balancing of intermittent production of electrical power from (e.g.) solar and wind. This proposal aims to characterise a promising cathode material for future sodium-ion batteries, Na1-xMnO2. The electrochemical performance of Na0.7MnO2-x has been previously related to its defect structure, including cation/vacancy ordering and oxygen non-stoichiometry. However, these studies have relied on X-ray radiation, which is unsuitable for determining light elements' atomic positions and occupancies. We would like to collect neutron powder diffraction data on Polaris as a function of temperature and gas atmosphere for a phase-pure Na0.7MnO2 sample. This will provide important information on the thermodynamic stability of the various phases, the Na-ion mobility and the oxygen deficiency of the material under different conditions.