Electrochemical Properties of Titanium Oxides with Disordered Layer Stacking through Flocculation of Exfoliated Titania Nanosheets

A new type of layered titanium oxides with turbostratic stacking has been synthesized via flocculation of exfoliated titania nanosheets with HCl or LiOH. Nitrogen adsorption–desorption isotherms showed that the spray-dried flocculations had mesoporous structures composed of slit-shaped pores. Cross-sectional SEM and TEM analyses clarified that particles were composed of agglomerated highly twisted flakes. UV-Visible diffuse reflectance spectra of restacked titania nanosheets were depended on the restacking process and were significantly blue shifted compared with that for the parent layered compound. The product flocculated with HCl showed a high initial capacity of about 300 mAh g−1 (cutoff voltage: 1.0 V), whereas rechargeable capacities were gradually decreased during charge-discharge repetition. On the other hand, the heat-treated product restacked by LiOH showed a relatively good cyclability over the 50 cycles, indicating a rechargeable capacity of about 150 mAh g−1. X-ray absorption spectra and cyclic voltammograms gave the evidence of the redox reaction of titanium, and the average voltage depended on the type of layer stacking. The XRD analyses of electrodes after charge-discharge revealed that the cyclability depended on the stability of layer structure.