The lithium-ion battery (LIB) is a promising device for the delivery of the energy and power required for a wide variety of applications ranging from portable electronics to electrical vehicles space. In this context, SnO2-or Sn-based materials display a high reversible capacity of nearly 781 mA hg À1 (theoretical), which is more than double that of commercial graphite (372mAhgÀ1).[1] However, large volume changes (% 300%) leading to widespread particle disintegration in Sn/SnO2 result in poor cyclability.[2] One approach towards tackling this issue has been the incorporation of an optimized pore structure inside the grains of Sn/SnO2. Another novel and effective strategy to improve the cyclability of SnO2 is to electronically wire it with conductive components, such as carbon. Usually, amorphous carbon is employed for wiring. However, this has been observed to be not very effective, mainly because the carbon coverage on SnO2 is unable to maintain a percolative contact (for electrons) between the disintegrated SnO2 grains.[3] In this regard, a better approach would to be employ extended carbon structures, such as carbon nanotubes (CNTs)[4] or graphene.[5] Graphene in particular exhibits extraordinary physical properties, such as high electrical conductivity and good mechanical strength.[6] In the same light, oxides of graphene have also been employed as electronic wires to improve the battery performance of various anodes (TiO2, Co3O4, SnO2).[7] Most importantly, published reports employ very large amounts (% 10–40 wt%),[7d, 8] of graphene/graphene oxide to improve the electrochemical properties of the oxide anodes. This is detrimental because it may affect the packing density of the material and lead to poor cyclability. Herein, we demonstrate an enhancement in the electrochemical performance of mesoporous SnO2 by using very low amounts (1% by weight) of reduced graphene oxide (rGO). Even such a low concentration of rGO is sufficient to provide efficient electronic pathways during charge/discharge of the cell. The other feature of this work is the demonstration of reversible lithium storage in SnO2/SnO over several cycles.

The SnO2-rGO composite was synthesized by using a twostep solution-phase hydrothermal process (see the Supporting Information, Materials Synthesis section). The graphite oxide (abbreviated as GO) employed here was synthesized by using the Hummers method.[9] An appropriate amount of graphite oxide (GO) was then dispersed in ethanol by sonication to give graphene oxide. An appropriate amount of aqueous SnCl2· 2H2O was added (acidic pH) and the mixture was transferred to a stainless steel autoclave for the hydrothermal reaction. The black product obtained following the hydrothermal reaction was centrifuged and washed, then aqueous SnCl2· 2H2O was added (acidic pH) and the mixture was transferred to a stainless steel autoclave for the hydrothermal reaction. The black product obtained following the hydrothermal reaction was centrifuged, washed, and finally calcined in air. The one-pot synthesis procedure converted graphene oxide to reduced graphene oxide (rGO).[7d] Evidence of rGO can be seen from Raman spectroscopy measurements (Lab RAM HR; λ= 514 nm; Supporting Information Figure S1). For SnO2-rGO, G and D bands are observed at 1598 and 1340 cmÀ1, respectively.[10] The ratio of D to G bands was approximately 1.8. Bare SnO2 nanoparticles were synthesized under identical experimental conditions except for the addition of GO. The samples with and without GO are abbreviated as SnO2-rGO and SnO2 respectively. Inclusion of rGO in small amounts (1%; estimated by using …