Lithium intercalation behavior into iron cyanide complex as positive electrode of lithium secondary battery

Lithium intercalation of iron cyanide Prussian blue, Fe ₄[Fe(CN) ₆] ₃· xH ₂O, in an aprotic media was examined in regard to the water content inside the lattice. Prussian blue showed reversible lithium intercalation potential around 3 V vs. Li, which corresponds to a redox of iron ions. Two types of water molecules were contained in the structure, one of which called zeolitic water has little effect on lithium intercalation and the theoretical capacity was always observed regardless of its amount. Other coordinating water molecules surrounding Fe ³⁺ ions were necessary for the lithium intercalation and their removal by drying beyond 200°C led to a significant capacity decrease.