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

• A bilayer strategy is explored to improve the performance of Si nanoparticles as anode materials. • Anatase TiO 2 layer on the surface of Si nanaparticles retards the regrowth of the SEI film. • The wrapping sheets of graphene play roles as conductive pathways and flexible micro-collectors. Pomegranate shaped microspheres consisting of Si nanoparticles coated with a TiO 2 shell and wrapped with reduced graphene oxide sheets (Si@TiO 2 @rGO) have been designed and fabricated. A sol–gel method is applied to coat the Si nanoparticles with a TiO 2 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 TiO 2 shows a higher strength to withstand the structural deformation of Si. The new phase derived from the TiO 2 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@TiO 2 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@TiO 2 @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 .