Facile controlled growth of silica on carbon spheres and their superior electrochemical properties

In this paper, silica coated carbon sphere composites were synthesized by a facile hydrothermal method. During the preparation, carbon@silica composites were formed by hydrolysis and deposition of TEOS on the surface of carbon spheres. XRD patterns show that this coating layer is composed of crystallized SiO2. When different amounts of TEOS were added, carbon@silica composites show different surface morphologies formed by silica nucleation and growth, spreading into a thinly coated layer, repeatedly. These varied silica coating layers have a great effect on the SEI film formation and electrochemical properties of the carbon@silica composites. The surface morphology and onset formation voltage of the surface film are greatly dependent on the surface morphology and structure of carbon@silica composites. Similarly, the lithiation and delithiation behaviors are obviously affected by this silica coating layer. Carbon@silica composites can deliver a reversible capacity of 351 mAh·g−1 in 0.0–3.0 V after 30 cycles, which is higher than that of the pristine carbon spheres. The extra capacity mainly comes from the Li-storage in the micropores and disordered graphene layers after silica coating. By broadening the electrochemical cycling window, a higher reversible capacity of 511 mAh·g−1 can be delivered in the voltage range between −15 mV and 3.0 V. The excess capacity in the low voltage region is mainly associated with additional Li-storage in micropores. It indicates that carbon@silica composites are promising anode materials for lithium-ion batteries.