Crystal chemistry of Na insertion/deinsertion in FePO4-NaFePO4

In this paper we examine the mechanism of Na insertion and extraction in the FePO4-NaFePO4 system. Chemical preparation of the intermediate Na1-xFePO4 phase has revealed the existence of a range of stable compositions with different Na+/vacancy arrangements. The mechano-chemical aspects of the charge and discharge reactions are also discussed.