Cathode properties of pyrophosphates for rechargeable lithium batteries

Two rechargeable pyrophosphates, LiVP 2O 7 and TiP 2O 7, were synthesized by a solid state reaction, and the cathode properties were investigated. The structures were characterized by powder X-ray Rietveld refinement. LiVP 2O 7 was isostructural with P2 1 monoclinic LiFeP 2O 7 and TiP 2O 7 was isostructural with Pa3 cubic ZrV 2O 7. Lithium cells using LiVP 2O 7 cathodes showed that approximately 0.5 Li per unit could be reversibly deintercalated from LiVP 2O 7 at 4.1 V vs. Li/Li +. On the other hand, 0.6 Li per unit could be reversibly intercalated into TiP 2O 7 at 2.6 V vs. Li/Li +.