Cathode properties of pyrophosphates for rechargeable lithium batteries

Two rechargeable pyrophosphates, LiVP2O7 and TiP2O7, were synthesized by a solid state reaction, and the cathode properties were investigated. The structures were characterized by powder X-ray Rietveld refinement. LiVP2O7 was isostructural with P21 monoclinic LiFeP2O7 and TiP2O7 was isostructural with Pa3 cubic ZrV2O7. Lithium cells using LiVP2O7 cathodes showed that approximately 0.5 Li per unit could be reversibly deintercalated from LiVP2O7 at 4.1 V vs. Li/Li+. On the other hand, 0.6 Li per unit could be reversibly intercalated into TiP2O7 at 2.6 V vs. Li/Li+.