As a new molecular cluster cathode material for lithium batteries, K5.72H3.28[PV14O42] (KPV), a hetero polyoxovanadate with a bi-capped Keggin structure, was synthesized. Its crystal structure was refined by X-ray Rietveld analysis, and its electrochemical properties were examined. The symmetry space group of KPV was assigned to FM3-M. The [PV14O42](9-) bi-capped Keggin units are connected sharing K+ ions. KPV contains many cation site vacancies and has tunnels facing various directions. The polycrystalline KPV powder becomes amorphous when dried at 80 degrees C. while the molecular cluster structure of KPV, identified by Raman scattering method, is maintained. KPV showed higher discharge capacity with higher discharge voltage than K-3[PMo12O40] (KPM) with Keggin-type structure. The most improved property of KPV compared with KPM was cycle stability. KPV kept 95% of its initial discharge capacity after 50 cycles of discharge-charge, whereas KPM kept only 35%. The presence of bi-capped Keggin unit is confirmed by ex situ EXAFS measurement, even though a rapid amorphization of KPV was observed at the beginning of the discharge-charge process in ex situ X-ray diffraction (XRD) measurements. The results of ex situ EXAFS measurement and the reversible charge transfer resistance of KPV estimated from the AC-impedance measurement during the discharge-charge process also indicate that the cycle stability of KPV is attributable to the stability of the KPV cluster ion unit. (C) 2012 Elsevier By. All rights reserved.