Ion Exchange of Layer-Structured Titanate Cs<sub>x</sub>Ti<sub>2</sub>-<i><sub>x</sub></i>/<sub>2</sub>Mg<i><sub>x</sub></i>/<sub>2</sub>O<sub>4</sub> (<i>x</i> = 0.70) and Applications as Cathode Materials for Both Lithium- and Sodium-Ion Batteries

Abstract

Cathode materials for rechargeable batteries have been extensively investigated. Sodium-ion batteries are emerging as alternatives to lithium-ion batteries. In this study, a novel cathode material for both lithium- and sodium-ion batteries has been derived from a layered crystal. Layer-structured titanate CsxTi2-x/2Mgx/2O4 (x = 0.70) with lepidocrocite (γ-FeOOH)-type structure has been prepared in a solid-state reaction from Cs2CO3, anatase-type TiO2, and MgO at 800°C. Ion-exchange reactions of Cs+ in the interlayer space were studied in aqueous solutions. The single phases of Li+, Na+, and H+ exchange products were obtained, and these were found to contain interlayer water. The interlayer water in the lithium ion-exchange product was removed by heating at 180°C in vacuum. The resulting titanate Li0.53H0.13Cs0.14Ti1.65Mg0.30O4 was evaluated for use as cathodes in both rechargeable lithium and sodium batteries. The Li+ intercalation-deintercalation capacities were found to be 151 mAh/g and 114 mAh/g, respectively, for the first cycle in the voltage range 1.0 - 3.5 V. The amounts of Li+ corresponded to 0.98 and 0.74 of the formula unit, respectively. The Na+ intercalation-deintercalation capacities were 91 mAh/g and 77 mAh/g, respectively, for the first cycle in the voltage range 0.70 - 3.5 V. The amounts of Na+ corresponded to 0.59 and 0.50 of the formula unit, respectively. The new cathode material derived from the layer-structured titanate is non-toxic, inexpensive, and environmentally benign.