Ion Exchange of Layer-Structured Titanate Cs_xTi₂-<i>_x</i>/₂Mg<i>_x</i>/₂O₄ (<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 Cs x Ti 2 - x / 2 Mg x / 2 O 4 ( x = 0.70) with lepidocrocite ( γ -FeOOH)-type structure has been prepared in a solid-state reaction from Cs 2 CO 3 , anatase-type TiO 2 , 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 Li 0.53 H 0.13 Cs 0.14 Ti 1.65 Mg 0.30 O 4 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.