2010 年 78 巻 5 号 p. 431-434
Li+ ion insertion/extraction properties of TiO2(B) powder, which was prepared from a K2Ti4O9 precursor by ion-exchange and dehydration, was investigated as a high-potential negative electrode. The irreversible capacity greatly decreased from 124 mAh g−1 to ca. 40 mAh g−1 when the lower potential limit was raised from 1.0 V to E≥1.2 V, which indicated that the irreversible capacity mainly originated from surface reactions, such as solvent decomposition, at E≤1.2 V in the first cycle. In galvanostatic intermittent titration tests, large polarization was observed at the beginning and the end of charging. This clearly indicated that a slow process is involved in the insertion reaction at the beginning and the end of charging, which causes solvent decomposition at potentials lower than 1.4 V. The reversible capacity was greatly improved to 246 and 276 mAh g−1 at an elevated temperature of 60°C and at a lower rate of C/60, respectively. The TiO2(B) sample contained ca. 14 wt% of the anatase phase as an impurity, and a reduction of the anatase phase was found to be effective for an increase in reversible capacity at moderate charge/discharge rates.
