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

Abstract

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.