The insertion of lithium in vanadium pentoxide at high temperature is followed both by Xray diffraction and Li-7 NMR studies. A correlation between the lithium sites found by structure determination and the isotropic chemical shifts is established and a mechanism of the lithium insertion proposed. Calculations of the valence of the vanadium atoms and the simulation of NMR spectra allows to localise the V4+ in the highest lithium rate phases.