Studies on Nano-CaO•SnO2 and Nano-CaSnO3 as Anodes for Li-Ion Batteries

The nanocomposite CaO center dot 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 center dot SnO2 and particles of similar to 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 center dot 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 center dot 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-CaSnO3 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 center dot SnO2 in comparison to nano-CaSnO3 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 (D-Li+) estimated from EIS is similar to 1.0 x 10(-14) cm(2) s(-1) at V <= 1.0 V during the first cycle and 11th discharge cycle.