Abstract
Nowadays, the society of highly dependent with electrical technologies is facing with seriously environmental pollution, over-consumption of limited fossil fuel, climate changed by greenhouse gas effect. For sustainable life in the future most be based on the development of low carbon footprint and high efficient energy storage. Since 1990s, Li ion batteries (LIBs) have been considered as high potential energy conversion due to the merits of chemical stability, higher capacity, longer lasting recharging, optimal operating potential and portable weight. For commercialization, graphitized carbon is commonly used as anode material, but there is a knotty problem of very low theoretical and experimental capacity for useless applying to high speed calculation and/or electric vehicles. In the past decade, Sn-based materials have been chosen as active materials for anode of LIBs because of its high theoretical capacity, abundant, easily synthesizing and low price. On the other hand, fabricating with the ordered mesoporous carbon spheres (OMCS) seems useful to buffer the huge volume change of Li-Sn formation due to their high surface area, hierarchical porous structures and good conductivity, resulting to stabilizing the microstructures and increase the cycle life. Herein, it was focused on the fabrication of various tin-based materials involved Sn, SnO and SnO2 composited with OMCS and further to estimate the electrochemical performances for Li storage in this study. At first, a series of OMCS has been successfully synthesized with various diameters of 50, 90 and 130 nm via an environmentally benign, most effective and conventional hydrothermal method. The physical and chemical properties of OMCS have been evaluated by performing scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption analysis, small-angle scattering system (SAXS), X-ray diffraction (XRD), Raman spectroscopy and electrochemical performances of coin type cell for Li storage. The results show that the OMCS with largest size has wide distribution of diameters and exhibit high specific capacity of 560 mA h g-1 at 0.1 C and 240 mA h g-1 at 5 C attributed by i) coexistence of mesopores and macropores for facilitating Li+ diffusion and ii) highest micropore surface area for increase of Li storage. Various SnOx (x = 0-2) nanoparticles with various Sn/C ratio from 5 to 35 wt% composited OMCS have been successfully fabricated by the simple and green process of microwave assisted hydrothermal method. The present work followed the same physiochemical and electrochemical analysis. The SnO2/OMCS composite with highest Sn/C ratio (35 wt%), highly ordered mesoporous structure, smaller particles size of SnO2 (3-6 nm) and nanoscale composite (approximately 120 nm) exhibited high reversible capacity of 1122-293 mA h g-1 under the current densities of 35-3500 mA g-1 for 75 discharge-charge cycles. Also, the first coulombic efficient was significantly increased from 40% to 60% resulting to decrease the irreversible capacity in 1st cycle. Furthermore, it shows 400 mA h g-1 under ultra-high current density of 3500 mA g-1 for as longer as 400 cycles. Before and after cycles, the results from TEM images exhibited the uniform nanocomposites with Sn particles sizes of 5-10 nm and maintenance of spherical carbon with ordered mesopores. As excellent LIBs performance of SnO2/OMCS nanocomposites was contributed by rapid charge transfer, stable SEI layers and minimizing polarization effects carried out from highly integrated hierarchical pores and closed packing morphology between inter SnO2 nanoparticles with optimization of Sn loading amounts.