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.
Highlights
IntroductionWe have studied the characterizations of layer-structured titanates with lepidocrocite (γ-FeOOH)-type structure [1]-[7]
The interlayer water in the lithium ion-exchange product was removed by heating at 180 ̊C in vacuum
We have studied the characterizations of layer-structured titanates with lepidocrocite (γ-FeOOH)-type structure [1]-[7]
Summary
We have studied the characterizations of layer-structured titanates with lepidocrocite (γ-FeOOH)-type structure [1]-[7]. We reported that the Li+ exchange product of Li2Ti5O11, derived by the ion-exchange reaction from layer-structured titanate Cs2Ti5O11, exhibited discharge-charge capacities of 120 and 100 mAh, respectively, for the first cycle in a rechargeable sodium battery in the voltage range 0.70 - 4.0 V [8]. These discharge-charge capacities obviously correspond to a Ti4+/Ti3+ redox couple in the layer-structured titanate.
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