Lithium intercalation behavior of iron cyanometallates

Iron cyanometallates having a formula, M6−mn+[Fem+(CN)6]n (M=V, Mn, Co, Ni, Cu) were prepared and their charge–discharge behavior was discussed. In the V–Fe complex, average discharge potential is about 3.6 V corresponding to reduction of V3+, whereas the Mn, Co, Ni, and Cu complexes show similar discharge potential around 3.3 V that is resulted from reduction of [Fe3+(CN)6]3− unit in the lattice. The specific capacity of V, Mn, Co, Ni complexes show about 60–80 mA h g−1, but copper complex indicates almost double capacity, ca. 140 mA h g−1. This is explained by considering the capacity caused by Cu2+ to Cu+ reduction in addition to [Fe3+(CN)6]3−→[Fe2+(CN)6]4− reduction.