Studies on nano-CaO·SnO2 and nano-CaSnO3 as anodes for Li-ion batteries

Abstract

The nanocomposite "CaC·SnO2" and nano-CaSnO3 are prepared by the thermal decomposition of CaSn(OH)6 precursor and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HR-TEM) along with selected area electron diffraction (SAED) and density measurements. Nanosize (3-6 nm) grains of CaO and SnO2 in the X-ray amorphous CaO·SnO2 and particles of ∼60 nm size in nano-CaSnO3 are obtained. Galvanostatic cycling of both the phases vs Li metal is performed in the voltage ranges 0.005-1.0 V and 0.005-1.3 V at the current rate, 60 mA g-1 (0.12 C). Stable and reversible capacities of 490 (±5) and 550 (±5) mA h g-1 are observed for nano-CaO·SnO2 respectively up to 50 cycles in the above voltage windows. These values correspond to 3.8 and 4.2 mol of cyclable Li per mole of CaO·SnO2 in comparison to the theoretical value of 4.4 mol of Li. A capacity of 420 (±5) mA h g-1 is observed at a rate of 0.4 C. Nano-CaSn03 showed a stable capacity of 445 (±5) mA h g-1 (3.4 moles of Li) up to 50 cycles when cycled in the voltage window, 0.005-1.0 V. The average discharge and charge potentials are 0.2 V and 0.5 V, respectively, for both the phases. The reasons for the superior Li-cycling performance of nano-CaO ·SnO2 in comparison to nano-CaSnO 3 are discussed. Ex situ XRD, TEM, and SAED studies are carried out to support the reaction mechanism. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) data as a function of voltage are presented and discussed to complement the galvanostatic results. The "apparent" Li-ion diffusion coefficient (DLi+) estimated from EIS is ∼1.0 × 10-14 cm2 s-1 at V ≤ 1.0 V during the first cycle and 11th discharge cycle. © 2008 American Chemical Society.