Link between thermal behaviour, positions of structural water and sodium content in low vacancy Prussian white

The iron and sodium based Prussian Blue analogue, Na2-xFe[Fe(CN)6]y.zH2O (PW) is a highly promising positive electrode material for sodium ion batteries. A large amount of research has focused on producing Prussian White with a low water (z) and vacancy (y) content in order to ensure both a high sodium ion storage capacity and a long cycle lifetime. In the low vacancy samples, water removal typically occurs over a narrow temperature range around 200C. However, this temperature appears to be strongly dependent on the sodium content. As water removal from the structure is vital to ensure good performance, understanding the structural relation between water removal temperature and cation content is important to understand in order to develop procedures for treating the material prior to application in a non-aqueous battery.