Amorphous Cobalt Selenite Nanoparticles Decorated on a Graphitic Carbon Hollow Shell for High-Rate and Ultralong Cycle Life Lithium-Ion Batteries

Transition metal compounds with complex compositions forming heterointerfaces during cycling are under development on account of their excellent electrochemical properties. Herein, a new synthesis strategy is successfully developed for uniquely structured hollow carbon nanospheres comprising amorphous CoSeOx nanoparticles. A drop-and-dry infiltration method is applied to synthesize metal salt-infiltrated hollow carbon nanospheres, which are then posttreated with a metalloid Se under inert conditions to form CoSe2-C hollow nanospheres. Partial oxidation of these nanospheres under a 350 °C air atmosphere produces amorphous CoSeOx-C hollow nanospheres. The synthesis of amorphous metal selenite using conductive carbon is being reported here for the first time. Moreover, the conversion mechanism of amorphous CoSeOx is studied systemically via ex situ X-ray photoelectron spectroscopy, transmission electron microscopy, and electrochemical analyses. The amorphous characteristics and heterostructure formation and the graphitic carbon with a good electric conductivity contribute to the good electrochemical kinetic performance and ultrastable cyclic stability of CoSeOx-C. CoSeOx-C shows remarkable long-term cycle performance (799 mA h g-1 for the 3000th cycle at a high current density of 5.0 A g-1) as well as remarkable rate capability (691 mA h g-1) even at 30 A g-1.