Preparation of silicon nanoball encapsulated with graphene shell by CVD and electroless plating process

Carbon materials such as graphite have been widely used as the anode materials of secondary batteries. In spite of good stability, they are limited by low capacity. Silicon has a 4 times higher capacity than any other carbon material. But it cannot be used, because it has a low stability caused by the volume expansion. In this study, we fabricated a silicon nanoball encapsulated with graphene (Si-GB) to overcome the mentioned problems. In order to form a core/shell structured graphene encapsulated silicon nanoball, nickel was coated on the surface of a silicon nanoball by electroless plating method. Then, a graphene layer was synthesized on the surface of the nickel shell by a CVD process. We were able to make a Si-GB by etching the nickel layer. The Si-GBs were formed with a spherical void between the silicon particle and the graphene layer, by which it has a better safety against to volumetric change of anode during lithiation/delitiation of repeated charging-discharging in secondary batteries. Morphology of the graphene encapsulated silicon nanoball was observed by the field emission scanning electron microscope (FESEM) and the field emission transmission electron microscope (FETEM) to find core-shell structured nanoball. Spherical structure of graphene encapsulated silicon nanoball was investigated by the Raman, the X-ray Photoelectron Spectroscopy to identify graphene layer on the surface of the inner silicon core. The charge-discharge performance of the Li-ion battery using Si-GB was investigated by the battery cycler system.