|(a) SEM image and (b) TEM image of the as-prepared SnO2 nanosheets. Source: Wang et al./ACS. Click to enlarge.
A team of researchers from Zhejiang University (China) and the Austrian Academy of Sciences has successfully synthesized a new SnO2 nanoarchitecture: extremely thin sheets, with minimum thicknesses of 1.5-3.0 nm. The assemblies of these sheets have a high BET surface area of 180.3 m2/g and extraordinarily large pore volume of 1.028 cm3/g.
The sheets exhibit a high lithium storage capacity and excellent cyclability due to the nanometer-sized frame and breathable characteristic, making them a promising candidate for a higher capacity lithium-ion anode material. A paper on their work appeared online 9 December in the Journal of the American Chemical Society.
With a high theoretical gravimetric lithium storage capacity of 782 mAh g-1—more than twice that of the currently commercialized graphite (372 mAh g-1)—and low potential of lithium ion intercalation, SnO2 is regarded as a promising anode material for lithium-ion batteries.
Tin oxides, however, can suffer from severe capacity loss, first due to a formation of electrochemically inactive Li2O during the first few cycles and then due to pulverization stemming from drastic volume changes.
To enhance the cyclability of the electrode, hybridizing SnO2 with carbon is effective, but this approach sacrifices the capacity itself due to the introduction of carbon and is usually complicated in fabrication. It is suggested that if single SnO2 was used as an active material, it should be in a nanometer-sized frame to shorten the pathway lengths of the lithium ion and should possess interior hollow spaces to accommodate large volume change. Herein, we report highly porous SnO2 nanometer-sized sheets synthesized from a hydrothermal reaction.—Wang et al.
Performance tests of the material as a lithium-ion anode material found that it exhibited a high discharge capacity of 559 mAh g-1 after 20 cycles with the retention of 57%. The Coulombic efficiency kept steadily at more than 95%.
Recently, Park et al. reported a SnO2/graphene hybridization, which also exhibited enhanced cyclic performance. The introduction of graphene plays dual roles; i.e., it increases the electrode conductivity and acts as a buffer layer to contain stresses induced by volume change. In comparison, the charge capacity of SnO2/graphene remains ~593 mAh g-1 after 20 cycles which is slightly higher than our results of 559 mAh/g. Nevertheless, considering we applied a wider cutoff window and larger constant current which are prone to create relatively harsher destruction and resistance of the electrode, the material reported here is very attractive due to its facile, economical, and high purity synthesis. Its performance via hybridization will be further studied.—Wang et al.
Cen Wang, Yun Zhou, Mingyuan Ge, Xiaobin Xu, Zaoli Zhang and J. Z. Jiang (2009) Large-Scale Synthesis of SnO2 Nanosheets with High Lithium Storage Capacity. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja909321d