Electrochemical intercalation of lithium into hexagonal tungsten trioxide

The kinetics and thermodynamics of electrochemical intercalation of lithium into hexagonal WO3 prepared by a solution technique were studied with an a.c. impedance method, open-circuit potential and X-ray diffraction measurements. The open-circuit potential-x in LixWO3 curve consists of two straight lines with different slopes, which was related to the structural variation in the oxide with lithium intercalation. The standard Gibbs energy of lithium intercalation, Delta G(l)(0), was -239.4 kJ/mol in the range of x from 0 to 1 in LixWO3 at 25 degrees C. The chemical diffusion coefficient of lithium, (D) over tilde, for the intercalation into the oxide, was measured by a.c. impedance method as functions of depth of lithium intercalation and temperature in 1 M LiClO4/propylene carbonate solution. The results showed that the Warburg impedance was linearly related to omega(-1/2) (omega: angular frequency) and the ((D) over tilde) values obtained decreased with an increase in lithium concentration in the oxide, being one-two orders of magnitude higher than that in monoclinic WO3. Furthermore, the lithium diffusion coefficient of lithium and the activation energy for the diffusion were also obtained as a function of x-value in LixWO3.