Lithium insertion in α I -VOPO 4 and α I I -VOPO 4 , either by chemical or electrochemical route, leads to the same new compound: α I -LiVOPO 4 (space group P4/nmm). The structure, resolved by neutron and synchrotron diffraction, is made up of planes of corner-connected PO 4 and VO 5 polyhedra, whereas lithium atoms are located between the layers. The reversal of the short vanadyl bond that corresponds to the insertion-induced α I I -α I transition finds an explanation in terms of lattice energy. It favors the migration of lithium ions in the (001) interlayer planes, a key parameter for the electrochemical performance as electrode material in Li-ion batteries.