Li intercalation in 2D iron phosphate synthesized from the partial dehydration and deprotonation of vivianite

This study focuses on the cation intercalation of structurally unique compounds synthesized from the partial dehydration and deprotonation of coordinated water molecules in hydrous materials. Partial dehydration can potentially result in hydrous materials with a porous nature, which maintains the parent structure of the material, and deprotonation causes oxidation in the hydrous materials. Li-intercalation experiments were conducted on the hydrous iron(II) phosphate mineral, vivianite (Fe2+3(PO₄)₂·8H₂O), and its oxidized and partially dehydrated product, santabarbaraite. Vivianite comprises two-dimensional Fe₃(PO₄)₂ sheets and coordinated water molecules. The oxidation progress of the Fe²⁺ of vivianite increased cathodic capacities up to 156 mA h g^-1. The Li-intercalation reaction rate increased significantly owing to dehydration because the partial dehydration of vivianite created structural space for the diffusion of Li⁺. Furthermore, X-ray diffraction measurements revealed that Li intercalation did not cause the formation of byproducts.