Key points are not available for this paper at this time.
Abstract An alluaudite‐type sodium iron sulfate has recently been discovered as a 3.8 V cathode material for low‐cost, high‐power, and efficient sodium‐ion batteries. To optimize the composition of the alluaudite phase and to explore further compounds, we have carefully surveyed the Na 2 SO 4 ‐FeSO 4 binary system. Solid‐state reactions at a moderate temperature of 623 K produce two stable phases: 1) vanthoffite‐structured Na 6 Fe(SO 4 ) 4 and 2) alluaudite‐type Na 2+2 x Fe 2− x (SO 4 ) 3 with a certain non‐stoichiometry. The possible compositional and structural flexibilities demonstrated in this work inspire further improvement of the alluaudite‐type sodium metal sulfates for advanced sodium‐ion batteries.
Oyama et al. (Wed,) studied this question.