Electrochemical lithium intercalation into WO3 and lithium tungstates LixWO3+x/2 of various structures

Abstract

Hexagonal and monoclinic tungsten trioxides WO3 and hexagonal lithium tungstates LixWO3+x/2 (x = 0.10-0.42) from a soft chemistry route were used as the active cathode material in secondary lithium batteries. The hexagonal structures, regardless of their being an oxide or a tungstate, showed higher specific capacities and better cycling behavior in Li+ intercalation reactions than the monoclinic form. The presence of pre-allocated lithium (as Li2O) in hexagonal tungstates decreased the capacity for lithium intercalation. Additionally, the plot of open-circuit voltage (OCV) against the depth of intercalation (n) for anhydrous tungstates showed two straight lines with different slopes that can be related to the structural changes in lithium intercalation. The effective diffusion coefficients of lithium insertion into the host structure, D̄, were also found to be dependent on the structure and the composition of these compounds.