Structure, and magnetic and electrochemical properties of layered oxides, Li2IrO3

Abstract

The layered oxide Li₂IrO₃ was synthesized and characterized by X-ray Rietveld analysis, and magnetic and electrochemical measurements. Li₂IrO₃ has a monoclinic cell similar to the Li₂RuO₃ structure. X-Ray Rietveld analysis showed that Li₂IrO₃ has a layered structure with different cation layers (Li only layers and layers of a mixture of Li and Ir) stacking alternately along the c axis and Ir hexagonal networks in successive LiIr₂ layers. In addition, it was shown that the degree (g) of formation of the Ir hexagonal network depended on the synthesis conditions and was close to complete Ir hexagonal at higher synthesis temperatures. Magnetic measurements showed that Li₂IrO₃ (g = 0.92) was antiferromagnetic with T_N = 15 K. Lithium de-intercalation from Li₂IrO₃ (g = 0.94) proceeded from monoclinic symmetry (Li₂IrO₃) to cubic (Li_0.5IrO₃) through orthorhombic symmetry (Li_1.0IrO₃). Electrochemical tests clarified that the Li/Li₂IrO₃ (g = 0.87) cell showed better cycling performance compared with the Li/Li₂IrO₃ (g = 0.94) cells. The Li/Li₂IrO₃ (g = 0.87) cells showed cycling capacities of 135 and 100 mA h g⁻¹ in the voltage range of 3.0–4.4 V and 3.0–4.2 V, respectively, and showed excellent cycling performance in the voltage range of 3.0–4.2 V.