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 · 2H₂O 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.