Iron(III) sulfate: a stable, cost effective electrode material for sodium ion batteries.

Iron(iii) sulfate, a rhombohedral NASICON compound, has been demonstrated as a sodium intercalation host. This cost-effective material is attractive, as it can be slurry processed in bulk with ball-milling, while utilizing the iron 2(+)/3(+) redox couple, offering stable 3.2 V performance for over 400 cycles.