A novel soft-chemical synthetic route using Na2Ti6O13 as a starting compound and electrochemical properties of H2Ti12O25

We have successfully prepared H2Ti12O25 by soft chemical synthetic technique using Na2Ti6O13 as a starting compound for the first time. In this synthetic route, we first prepared Li2Ti6O13 by Na+/Li+ ion-exchange reaction. Then, H2Ti6O13 was prepared by Li+/H+ ion-exchange reaction using HCl solution, and H2Ti12O25 was synthesized by heating the obtained H2Ti6O13 at 260 °C. The XRD pattern and 1H-MAS NMR spectrum of the H2Ti12O25 sample thus obtained were well consistent with those for the H2Ti12O25 sample prepared from Na2Ti3O7 as a starting compound. The H2Ti12O25 sample prepared from Na2Ti6O13 exhibited superior cycling performance with the initial discharge capacity of 229 mAh g−1 in the voltage range between 1.0 and 3.0 V with a fixed current density of 10 mA g−1 at 25 °C, which was higher than that (213 mAh g−1) for the H2Ti12O25 sample from Na2Ti3O7. The improvement of the discharge capacity may be explained by the smaller particle size for the present H2Ti12O25 sample. Accordingly, the initial coulombic efficiency for the H2Ti12O25 sample was improved from 86% to 92%. These facts suggest that H2Ti12O25 is one of the promising high-voltage oxide negative electrodes in advanced lithium ion batteries.