The new vanadium oxide, with the composition (Ca0.13K0.38V2.5V0.5O7.57)-V-IV-O-V.4.3H(2)O, has been prepared by electrochemical oxidation of the solid precursor CaV3O7 in aqueous KClO4 solution. The reaction mechanism is a two-phase transformation involving simultaneously calcium extraction, oxygen insertion, and Ca2+/K+ ion exchange. This poorly crystallized compound has a layered structure, with interlayer Ca2+, K+, and H2O, related to that of V2O5 xerogels and electrolytic V2O5 The anhydrous Ca0.13K0.38V3O7.57 compound reversibly intercalates 2.3 Li per formula unit (210 mAh g(-1)) at a slow rate in the 1.5-4 V range, whereas the CaV3O7 precursor does not intercalate any lithium under similar conditions. Preliminary cycling data indicate that the capacity depends on the cycling rate and decreases during cycling. (C) 2001 The Electrochemical Society. All rights reserved.