A deep investigation of amorphous V2O5-P2O5 powders for magnesium batteries communicates the vital properties to achieving the superior electrochemical performance at a 75 : 25 V2O5 : P2O5 molar ratio. The manipulation of the inter-layer spacing and amorphization of V2O5 can enhance Mg(2+) diffusion and afford a cathode with high-voltage reversibility.