Poly(3,4-ethylenedioxythiophene) Sheath Over a SnO2 Hollow Spheres/Graphene Oxide Hybrid for a Durable Anode in Li-Ion Batteries

SnO2 hollow spheres (HSs) were synthesized by a hydrothermal route by use of an organic additive (2-mercaptopropionic acid or MPA) and a cationic surfactant (cetyltrimethyl ammonium bromide or CTAB). The progressive transformation of SnO2 solid spheres to SnO2 HSs 140-150 nm in dimensions wherein a thin shell of densely packed SnO2 crystallites with a tetragonal crystal structure surrounds an empty core was followed by scanning- and transmission-electron microscopy. The roles of MPA as the HS structure-directing agent, CTAB as the moiety which prevents HS aggregation, and water as the solvent crucial for hollow core formation were independently determined by elaborate morphological analyses. With the goal of realizing superior electrochemical performance, hybrids of optimized SnO2 HSs embedded in graphene oxide (GO) nanosheets and enveloped by a sheath of a conducting polymer, poly(3,4-ethylenedioxythiophene) or PEDOT, were also synthesized; the continuity of the amorphous PEDOT coating on SnO2 HS/GO was confirmed by elemental mapping and X-ray photoelectron spectroscopy. Galvanostatic charge-discharge studies revealed an initial reversible capacity of 990 mA h g(-1) for SnO2 HSs at a current density of 100 mA g(-1), and a capacity of 400 mA h g(-1) was retained after 30 cycles. A significant improvement in cycling performance was achieved in the SnO2 HS/GO/PEDOT hybrid, as the synergy between the moderately high intrinsic electronic conductivity of GO nanosheets and the ability of PEDOT to buffer the volume change during repetitive Li+ charge discharge more efficiently compared to pristine SnO2 HS impart a capacity of 608 mA h g(-1) at a current density of 100 mA g(-1) to the hybrid, retained at the end of 150 cycles, and the latter value was similar to 1248 mA h when the mass of only the SnO2 HS in the hybrid was considered. The SnO2 HS/GO/PEDOT hybrid also showed an excellent rate capability as a capacity of 381 mA h g(-1) was attained even at a high current density of 2000 mA g(-1). We demonstrate the viability of the SnO2 HS/GO/PEDOT hybrid as a durable high performance anode for Li-ion batteries.