EPR of V-IV species is used to identify the different LixV2O5-phases (alpha, epsilon, delta, gamma) obtained by chemical intercalation of lithium in V2O5 and to study the evolution of V2O5 cathodes upon electrochemical lithium intercalation, which is characterized by two different behaviors depending on the composition range. For 0 < x < 1, the insertion is topotactic and reversible. For x > 1, the lack of reversibility arises from the gamma-phase and free VO2+ ions.