Hydrothermal synthesis of hexagonal tungsten trioxide from Li2WO4 solution and electrochemical lithium intercalation into the oxide

Tungsten trioxides with an open structure were synthesized by a hydrothermal reaction at 120–180°C 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=∼1 on discharge until 1.5 V vs. Li/Li+.