Graphene-wrapped yolk-shell of silica-cobalt oxide as high-performing anode for lithium-ion batteries

Silica (SiO2) shows promise as anode material for lithium-ion batteries due to its low cost, comparable lithium storage discharge potential and high theoretical capacity (approximately 1961 mA h g-1). However, it is plagued by issues of low electrochemical activity, low conductivity and severe volume expansion. To address these challenges, we initially coat SiO2 with CoO, followed by introducing SiO2@CoO into graphene sheets to fabricate an anode composite material (SiO2@CoO/GS) with uniformly dispersed particles and a 3D graphene wrapped yolk-shell structure. The coating of CoO on SiO2 converted the negative surface charge of SiO2 to positive, enabling effective electrostatic interactions between SiO2@CoO and graphene oxide sheets, which provided essential prerequisites for synthesizing composite materials with uniformly dispersed particles and good coating effects. Furthermore, the Co-metal formed during the charge-discharge process can act as a catalyst and electron transfer medium, activating the lithium storage activity of SiO2 and enhancing the conductivity of the electrode, conclusively achieving a higher lithium storage capacity. Ultimately, due to the activation of SiO2 by Co-metal during cycling and the excellent synergistic effect between SiO2@CoO and graphene, SiO2@CoO/GS delivers a high reversible capacity of 738 mA h g-1 after 500 cycles at 200 mA g-1. The product also demonstrates excellent rate performance with a reversible capacity of 206 mA h g-1 at a high specific current of 12.8 A g-1. The outstanding rate performance of SiO2@CoO/GS may be ascribed to the pseudo-capacitive contribution at high specific current upon cycling. The SiO2 was first modified by CoO coating and then introduced into graphene to fabricate composites with high dispersibility.