Template synthesis of graphitic hollow carbon nanoballs as supports for SnOx nanoparticles towards enhanced lithium storage performance

Abstract

To address the volume change-induced pulverization problem of tin-based anodes, a concept using hollow carbon nanoballs (HCNBs) as buffering supports is herein proposed. HCNBs with hollow interior, flexibility and graphitic crystallization are first prepared by a combined method of chemical vapor deposition (CVD) and template-synthesis using CH₄ as the carbon source and CaCO₃ as the conformal template. The ultrafine SnO₂ nanoparticles are loaded onto the HCNBs (denoted as SnO₂@HCNBs) via pyrolysis of tin(II) 2-ethylhexanoate at 300 °C in air. On further annealing SnO₂@HCNBs in Ar, SnO₂ is partially reduced to SnO_x by consuming a part of carbon of HCNBs as the reducing agent, and thus SnO_x@HCNBs are obtained (note that SnO_x represents a composite consisting of SnO₂, SnO and Sn phases). When applied as anode materials for lithium ion batteries (LIBs), HCNBs deliver high reversible capacities of 841 mA h g⁻¹ after 125 cycles at 200 mA g⁻¹, and 726 mA h g⁻¹ after 400 cycles even at 1000 mA g⁻¹, while SnO₂@HCNBs and SnO_x@HCNBs exhibit discharge capacities of 1042 and 1299 mA h g⁻¹ after 400 cycles at 200 mA g⁻¹, respectively. Notably, all of them display gradually increased capacity with retention over 100% even after long-term cycling, which is attributed to the novel robust characteristic of the HCNBs as revealed by the ex situ TEM analysis. The flexible hollow HCNBs with high graphitic crystallization not only efficiently tolerate the volume changes of the Li–Sn alloying–dealloying but also facilitate the electrolyte/charge transfer owing to the hollow structure and high conductivity of the HCNBs.