The Reaction Mechanism of Lithium Insertion in Vanadium Tetraphosphide

Lithium-free vanadium tetraphosphide was synthesized and electrochemical characterizations during cycling were carried out. Based on differential capacity plots (DCP) and X-ray analyses, a four-step reaction mechanism was suggested. The reaction sequences are topotactic lithium insertion into the , phase transformation from monoclinic to cubic phase, and VP formation by decomposition, and another lithium insertion into VP as the potential is lowered. Volume expansion of active material was expected from crystallographic data, and confirmed by scanning electron microscope observation during the second reaction step. In monoclinic sustaining range, showed an excellent cycling performance with a relatively large reversible capacity.