Synthesis, Structures, and Electrochemical Characteristics of Pyrophosphates

Abstract

We synthesized the two pyrophosphates LiVP_2O_7 and TiP_2O_7 by a solid state reaction, and the cathode properties of lithium secondary batteries were investigated. The structures were characterized by powder X-ray Rietveld refinement. Lithium cells using LiVP_2O_7 and TiP_2O_7 cathodes showed that approximately 0.5 Li per unit could be reversibly deintercalated from LiVP_2O_7 at 4.1V vs. Li/Li^+, 0.8 Li per unit could be reversibly intercalated into TiP_2O_7 at 2.6V vs. Li/Li^+. The redox potentials 4.1V of LiVP_2O_7 and 2.6V of TiP_2O_7 were higher than that of transition metal oxides such as VO_2 and TiO_2.