Sodium deintercalation from sodium iron oxide

Na ion deintercalation from α-NaFeO2 by charging a LiαNaFeO2 cell gives a new monoclinic phase, Na0.5FeO2. The room-temperature Mössbauer spectrum shows two kinds of doublet lines with almost same intensity. The isomer shifts are 0.33 and −0.07mm/s (relative to Fe metal), respectively, the former comes from Fe3+ state and the latter clearly originates in Fe4+ state. The trial of further deintercalation of Na ion brings the decomposition of the electrolyte and electrode. Discharge in LiNa0.5FeO2 cell is possible, but the Na ions remained hinders smooth lithium intercalation.