Abstract
The lithium intercalation properties of alkai tetratitanate (Li2Ti4O9·1.1H2O, Na1.5H0.5Ti4O9·0.53H2O) and octatitanate with various amounts of hydrated water (H2Ti8O17·nH2O; n = 0.41, 0.96, 1.5) were examined. Alkali tetratitanates were obtained by ion exchange of the starting tetratitanate hydrate (H2Ti4O9·1.9H2O) and subsequent heat treatment. Octatitanates were prepared by heat treatment of the starting tetratitanate hydrate. The prepared titanates exhibited a reversible capacity corresponding to a reduction of half of the Ti atoms from a tetravalent state to a trivalent state. This indicates that the reaction activity of the host oxide layer of titanates is not affected by the condensation reaction during transformation from tetratitanate to octatitanate. H2Ti8O17·0.41H2O showed the largest capacity and best rate capability among the prepared titanates; this is because of its relatively small chemical formula weight per Ti atom. The difference in the rate capability of the titanates is caused by the steric effects of hydrated water molecules in the lithium diffusion path along the b-axis.
