Effect of interlayer spacing on the electrochemical properties of alkali titanate nanotubes

Multilayered titanate nanotubes (TNTs) has been considered as a candidate for lithium ion battery anode material. However, it has a problem of high irreversible capacity due to trapped lithium ions in the interlayer space. To solve this problem, an attempt to enlarge the interlayer spacing has been made in this work to improve intercalation characteristics of TNTs. Monoatomic ions in hydrothermally heat-treated TNTs were substituted to one of Li, Na and K alkali ions via ion-exchange process. The TNTs (200) interlayer spacing peak in XRD patterns showed a shift to a lower angle, indicating an enlarged interlayer spacing of TNTs. The Li-, Na- and K-ion exchanged TNTs exhibited an initial capacity of 214, 230 and 248 mA h/g at 0.1 C, respectively, in the TNTs // LiPF6 electrolyte // Li metal coin type cell test. It was found that the enlarged interlayer spacing resulted in an increment in the specific capacity and rate capability. This increase was attributed to both the enhanced lithium ion diffusion and the increased number of lithium ion intercalation sites in the TNTs interlayers.