Journal of Physical Chemistry B, Vol.112, No.36, 11250-11257, 2008
Structural transformation of LiVOPO4 to Li3V2(PO4)(3) with enhanced capacity
In the present investigation, we report the transformation of alpha-LiVOPO4 to alpha-Li3V2(PO4)(3) leading to an enhancement of capacity. The alpha-LiVOPO4 sample was synthesized by a sol-gel method, followed by sintering at 550-650 degrees C in a flow of 5% H-2/Ar. The structural transformation of a triclinic alpha-LiVOPO4 structure to a monoclinic alpha-Li3V2(PO4)(3) structure was observed at higher sintering temperatures (700-800 degrees C in a flow of 5% H-2/Ar). The alpha-Li3V2(PO4)(3) phase was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, and X-ray absorption near edge spectrum (XANES) techniques. The valence shift of vanadium ions from +4 to +3 states was observed using in situ XANES experiments at V K-edge. The structural transformation is ascertained b the shape changes in prey edge and near edge area of X-ray absorption spectrum. It was observed that the capacity was enhanced from 140 mAh/g to 164 mAh/g via structural transformation process of LiVOPO4 to Li3V2(PO4)(3).