Tungsten trioxides with an open structure were synthesized by a hydrothermal reaction at 120-180 degreesC from an aqueous Li2WO4 solution at pH values from 0.5 to 2.0. The products contained some water molecules and Lithium ions, e.g. as x(Li2O) . WO3 . y(H2O) (x = 0.05-0.11, y - 0.6-0.8), and they formed at pH 0.5-1.0 and 1.5-2.0 with hexagonal and orthorhombic cells, respectively. The x value increased with increasing pH of the Li2WO4 solution and synthesis temperature. Electrochemical lithium intercalation into the tungsten trioxides was investigated in a LiClO4-propylene carbonate electrolyte solution. The x(Li2O) . WO3 . y(H2O) electrode underwent lithium intercalation up to Li/W = similar to1 on discharge until 1.5 V vs. Li/Li+. (C) 2000 Elsevier Science B.V. All rights reserved.