Anodic behaviour and X-ray photoelectron spectroscopy of ternary tin oxides

Abstract

The compounds SrSnO₃, BaSnO₃ and Ca₂SnO₄ have been synthesized by solid-state and/or sol-gel methods, characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) and their electrochemical properties studied as cathodes versus Li metal in the range 0.005-1.0 V. ASnO₃ (A = Sr, Ba), adopt the perovskite structure whereas Ca₂SnO₄ has the Sr₂PbO₄ structure. The discharge capacities (mAh g⁻¹) (moles of equivalent Li) on the 20th cycle at a current rate of 30 mA g⁻¹ are: SrSnO₃ (solid-state) (144 (1.4)), SrSnO₃ (sol-gel) (222 (2.1)), BaSnO₃ (solid-state) (190 (2.2)), BaSnO₃ (sol-gel) (156 (1.8)) and Ca₂SnO₄ (247 (2.4)). The SrSnO₃ (sol-gel) with nano-particle morphology displays better galvanostatic cycling performance than SrSnO₃ (solid-state). The cycling behaviour of SrSnO₃ and BaSnO₃ is inferior to that of Ca₂SnO₄ and CaSnO₃, which demonstrates that 'Ca' is superior as a matrix element than Sr or Ba. The inferior electrochemical performance of Ca₂SnO₄ in comparison to CaSnO₃ reveals that the higher Ca:Sn ratio in the former is not advantageous and the perovskite structure is preferable to that of Sr₂PbO₄ structure. The coulombic efficiencies are >98% in all cases. Cyclic voltammetry (CV) compliments the observed cycling behaviour.