Facile synthesis of ultrafine carbon-coated SnO₂ nanoparticles for high-performance reversible lithium storage

Ultrafine carbon-coated SnO₂ nanoparticles (NPs) with diameters of 3-6 nm are prepared by a hydrothermal method in the presence of ascorbic acid and subsequent thermal treatment. The ascorbic acid, on the one hand, serves as a ligand to control the growth of the ultrafine SnO₂ NPs during the hydrothermal process and on the other hand it acts as carbon precursor to form carbon shell surrounding the ultrafine SnO₂ NPs in the thermal treatment process. When evaluated as an anode material for lithium-ion batteries (LIBs), the as-synthesized ultrafine carbon-coated SnO₂ NPs exhibit a high reversible capacity of 688.6 mAh g^-1 at a rate of 1 C after 50 cycles. Even charging at the rate of as high as 5 C, they still deliver a reversible capacity of 414 mAh g^-1, which is about 50% of the theoretical capacity of SnO₂. The perfect electrochemical performance can be ascribed to the synergic effects of the conductive carbon shell surrounding the SnO₂ NPs and the ultra-small size of the SnO ₂ NPs.