Ultrathin SnO₂ nanosheets: Oriented attachment mechanism, nonstoichiometric defects and enhanced Lithium-ion battery performances.

We successfully synthesized large-scale and highly pure ultrathin SnO₂ nanosheets (NSs), with a minimum thickness in the regime of ca. 2.1 nm as determined by HRTEM and in good agreement with XRD refinements and AFM height profiles. Through TEM and HRTEM observations on time-dependent samples, we found that the asprepared
SnO₂ NSs were assembled by “oriented attachment” of preformed SnO₂ nanoparticles (NPs). Systematic trials showed
that well-defined ultrathin SnO2 NSs could only be obtained under appropriate reaction time, solvent, additive, precursor concentration, and cooling rate. A certain degree of nonstoichiometry appears inevitable in the well-defined SnO₂ NSs sample.
However, deviations from the optimal synthetic parameters give rise to severe nonstoichiometry in the products, resulting in the formation of Sn₃O₄ or SnO. This finding may open new accesses to the fundamental investigations of tin oxides as well as their intertransition processes. Finally, we investigated the lithium-ion storage of the SnO₂ NSs as compared to SnO₂ hollow spheres and NPs. The results showed superior performance of SnO₂ NSs sample over its two counterparts. This greatly enhanced Li-ion storage capability of SnO₂ NSs is probably resulting from the ultrathin thicknesses and the unique porous structures: the nanometer-sized networks provide negligible diffusion times of ions thus faster phase transitions, while the “breathable” interior porous structure can effectively buffer the drastic volume changes during lithiation and delithiation reactions.