Microspheres comprise Si nanoparticles modified with TiO₂ and wrapped by graphene as high-performance anode for lithium-ion batteries

Pomegranate shaped microspheres consisting of Si nanoparticles coated with a TiO₂ shell and wrapped with reduced graphene oxide sheets (Si@TiO₂@rGO) have been designed and fabricated. A sol–gel method is applied to coat the Si nanoparticles with a TiO₂ shell. An electrostatic interaction assisted spray drying process combined with a calcination step have been explored to achieve the wrapping of graphene and the formation of the pomegranate shaped microspheres. The layer of anatase phase TiO₂ shows a higher strength to withstand the structural deformation of Si. The new phase derived from the TiO₂ layer after the lithium embedding can acted as high-speed diffusion channels for lithium ions. The formation of the porous microspheres provided adaptive space for volume expansion of Si, while the wrapping of the Si@TiO₂ nanoparticles with flexible graphene relieves the internal stress and further improves the conductivity of the Si electrode. The synergistic effects of the bilayer endow the Si@TiO₂@rGO composite a superior reversible capacity of 1228.7 mAh g⁻¹ after 400 cycles at a current density of 0.5 A g⁻¹ and an excellent cycling stability of 776 mAh g⁻¹ after 1000 cycles at a high current density of 1 A g⁻¹.