Layered Alkali Metal Titanate with the Staging Structure and Superior Electrochemical Performance

We systematically explored the formation range of α-NaFeO₂-type layered titanate and its ion-exchange behaviors and electrochemical performance. The layered sodium titanate of Na_<i>x</i>Ti_1-<i>x</i>/3Li_<i>x</i>/3O₂ at <i>x</i> = 0.68-0.70 was synthesized by the solid-state reaction at 900 °C. The titanate is composed of coplanar host layers with the α-NaFeO₂-type structure. The interlayer Na⁺ ions underwent a facile exchange with other alkali metal ions in aqueous solutions at 80 °C, accompanied by concurrent exchange with proton/oxonium ions. Powder X-ray diffraction data on the products and their Rietveld refinement revealed the formation of a unique staging-structured titanate, in which the interlayer galleries are alternately occupied by incoming alkali metal ions and oxonium ions. The electrochemical intercalation-deintercalation properties for Li⁺ and Na⁺ ion storage were examined on the pristine sodium titanate and its ion-exchanged derivatives. The staging structure was found to provide superior electrochemical performance, which may be due to the rather open nature of the interlayer galleries, providing abundant sites for Li⁺ and Na⁺ ions.