Revealing ion substitution effects in Na[Li1/3Mn2/3]O2 with O3 structure for Na storage in batteries

Sodium ion batteries (SIBs) have energy densities close to lithium-ion batteries (LIBs) but can be based on overall more abundant elements. Compared to LIBs, the cathode chemistry of SIBs is much more diverse which provides opportunities but at the same time raises many fundamental questions. The most promising class of cathode materials are layered oxides whose redox behavior and phase behavior can be tuned by combining various (transition) metals. Despite the seemingly simplicity of these compounds, they show a highly complex and so far poorly understood behavior. This project aims at understanding, how the properties of layered Na[Li1/3Mn2/3]O2 with O3 structure can be tailored by Ca, Ni or Fe. The O3 structure provides a high Na content while Li acts as a structure stabilizer. Mn is attractive due to its abundance and is, along with the oxygen lattice, the redox active site. It is anticipated that partial substitution of Li and Mn with Ca, Ni or Fe has a strong effect on the properties of this compound, especially phase stability, conductivity, redox activity and storage capacity. Understanding these structure-property relationships requires the combination of experiments (synthesis, electrochemistry, various analytical tools incl. in situ / operando) and simulation (based on density functional theory calculations), which will be covered by the complementary expertise of the applicants.