Structure, physical properties, and charge-discharge characteristics of Fe-doped Li2IrO3

New layered oxides of Fe-doped Li2IrO3 were synthesized and characterized by X-ray diffractometry, Fe-57 Mossbauer spectroscopy, and magnetic and electrochemical measurements. All compounds had rhombohedral symmetry and adopted the alpha-NaFeO2-type structure. Fe-57 Mossbauer spectroscopy showed that Fe3+ is in the typical high spin state and Rietveld analysis of the X-ray diffraction data demonstrated that the octahedrally coordinated cation sites were occupied alternately along the c axis by Li+ only and by a mixture of cations (Li+, Fe3+, and Ir4+). The chemical formulas of Li1.8Ir0.6Fe0.6O3 (sample A! and Li1.79Ir0.50Fe0.70O3 (sample B) can be expressed as (Li)(3a)(Li0.2Ir0.4Fe0.4)(3)bO(2) and (Li)(3a)(Li0.2Ir0.333Fe0.467)(3)bO(2), respectively, while Li1.73Ir0.38Fe0.88O3 (sample C) can be expressed as (Li0.9675Ir0.0325)(3a)(Li0.1925Ir0.2205Fe0.5870)(3b)O-2. A Li/Li1.8Ir0.6Fe0.6O3 electrochemical cell possessed a capacity of 90 mAh/g, while the Li/Li1.75Ir0.5Fe0.75O3 and Li/Li1.696Ir0.391Fe0.913O3 cells had capacities of 43 and 5 mAh/g, respectively. Lithium deintercalation from Fe-doped Li2IrO3 was controlled mainly by changing the valence state of Ir from 4+ to 6+ and partly by oxidizing Fe from the 3+ to 4+ valence state during the first charge process. Initial irreversible capacity might be caused by structural change, corresponding to an increase in Ir valence state from 5+ to 6+. (C) 2003 The Electrochemical Society.