Electrochemical synthesis, characterization and lithium intercalation properties of e-MxV2O5+y.nH(2)O (M=Ni-II, Cu-II or Mn-IV)

The electrochemical oxidation of aqueous solutions of mixtures of VOSO4 and MSO4 (M = Ni, Cu or Mn) leads to solid deposits on the electrode, of gener al formulation MxV2O5+y. nH(2)O. These compounds present great similarities with the layered hydrated vanadic acids e-V2O5 obtained when oxidizing pur e VOSO4 solutions. In the case of solutions containing NiSO4 and CuSO4, the M2+ cations are incorporated, without any change in their oxidation state, into the interlayer space of the vanadic acid, thus replacing a part of th e exchangeable protons of e-V2O5. In the case of mixtures of VOSO4 and MnSO 4, there is simultaneous oxidation of Mn2+ and of VO2+, leading to a vanadi c acid in which the exchangeable protons of the interlayer space are replac ed by Mn-IV cations. As for e-V2O5 compounds, the electrochemical intercala tion of lithium into these compounds shows two main phenomena in the 4-2 V/ Li range. Among the title materials, the manganese-containing compound pres ents the largest reversible capacity (1.6 Li per formula unit in the 4-2 V/ Li voltage range at C/10), with the best cycling behavior. Whereas, by anne aling at 400 and 450 degreesC, respectively, the copper and nickel-containi ng compounds transform irreversibly to a mixture of alpha -V2O5 and MV2O6, annealing the manganese-containing compound at 300 degreesC leads to a new material structurally related to alpha -V2O5 but with a completely differen t lithium intercalation behavior. (C) 2001 Elsevier Science Ltd. All rights reserved.