Comparative Study of Electrochemical Performance of SnO2 Anodes with Different Nanostructures for Lithium-Ion Batteries.

Powders composed of SnO2 nanostructures including microporous nanospheres, mesoporous nanospheres and nanosheets were synthesized by the direct hydrothermal hydrolyzation of SnCl4, hydrothermal hydrolyzation of SnCl4 using glucose as a soft template and precipitation of SnCl2 ∙ 2H20 using oxalic acid as a precipitant, respectively. The electrochemical performance of the three samples used as the anode of a lithium ion battery was determined using galvanostatic discharge/charge tests and electrochemical impedance spectroscopy. Among of them, the anode composed of microporous SnO2 nanospheres demonstrated outstanding initial discharge and charge capacities of 2480 and 1510 mAh g-1, respectively, with a coulombic efficiency of 60.9% at a current density of 78 mA g-1 (0.1 C). In addition, high initial discharge and charge capacities of 1398 mAh g-1 and 950 mAh g-1, respectively, with a coulombic efficiency of 67.95% were obtained even at a high current density of 550 mA g-1 (0.7 C). Moreover, a reversible capacity of 500 mAh g-1 with a coulombic efficiency of 99.95% was attained even after 50 discharging/charging cycles at 550 mA g-1 (0.7 C). This superior electrochemical performance of the SnO2 anodes can be attributed to the large specific surface area (172.7 m2 g-1), small crystal size (approximately 15 nm) and the interstitial microporous pores (<2 nm) of the particles, which favored lithium-ion diffusion and insertion/desertion at the surface of SnO2 and decreased the polarization and the volume expansion of SnO2. Moreover, the resistance of the cell and Li+ diffusion coefficient were studied by electrochemical impedance spectroscopy.