SYNTHESIS AND ELECTROCHEMICAL STUDY OF NEW COPPER VANADIUM BRONZES AND OF 2 NEW V2O5 POLYMORPHS - BETA'-V2O5 AND EPSILON'-V2O5

The electrochemical properties of the high temperature three-dimensional beta-Cu0.6V2O5 and layered epsilon-Cu0.9V2O5 phases are reported. Copper can be partially or completely removed from these compounds at room temperature by means of strong oxidizing agents. Upon removal of the copper several new compounds with copper content below the high temperature thermodynamic range of equilibrium were obtained. For instance, two new polymorphs of V2O5; epsilon'-V2O5 with a two-dimensional structure and beta'-V2O5 with a three-dimensional structure were synthesized. All of these materials were tested as positive electrodes in room temperature secondary Li batteries. It was found that their performance strongly correlates with copper content. Within the beta-CuyV2O5 series it is the composition y = 0.05-0.1 that shows highest specific energy (750 Wh/kg) and the best cycling behavior. For the newly synthesized epsilon-CuyV2O5 series it is the composition y = 0.2 that shows the most promising electrochemical performance. Indeed, this material can reversibly intercalate up to 1.4 Li ions per vanadium atom at an average potential of 2.8 V, resulting in a theoretical specific energy of 1100 Wh/kg of cathode material, one of the highest theoretical energies ever reported.