Synthesis of hexagonal form of tungsten trioxide and electrochemical lithium insertion into the trioxide

Abstract

The tungsten trioxide hydrate, WO 3 · yH 2O ( y = 0.8−1.1) with the hexagonal tungsten bronze (HTB) structure has been prepared by acidification of lithium tungstate solution with strong acid at a concentration of 0.5–1 M and at a temperature of 100 °C. On the other hand, hydrothermal synthesis of an acidified lithium tungstate solution at temperatures of 150–200 °C leads to the formation of xLi 2O · WO 3 · yH 2O ( x = 0.25−0.30, y = 0.6−0.8) having the HTB structure. The dehydration of WO 3 · yH 2O and xLi 2O · WO 3 · yH 2O around 350 °C leads to the dehydrated trioxides, hexagonal WO 3 and xLi 2O · WO 3 with the HTB structure, respectively. The tungsten trioxides prepared have been characterized by X-ray diffractometry, thermogravimetric analysis and electrochemical method. The cyclic voltammetric and galvanostatic measurements revealed that a reversible lithium intercalation into the crystal lattice of hexagonal WO 3 takes place with charge-discharge cycling.