Graphene-encapsulated blackberry-like porous silicon nanospheres prepared by modest magnesiothermic reduction for high-performance lithium-ion battery anode

Porous silicon (Si) nanostructures have aroused much interest as lithium-ion battery anodes because of the large space to accommodate the volume change in lithiation and delithiation and shorter ion transfer distance. However, fabrication of porous structures tends to be difficult to control and complex, so, the final electrochemical performance can be compromised. Herein, a modest magnesiothermic reduction (MMR) reaction is demonstrated to produce blackberry-like porous Si nanospheres (PSSs) controllably using magnesium silicide (Mg2Si) as Mg source and SiO2 nanospheres as the reactant. This improved MR method provides good control of the kinetics and heat release compared to the traditional MR (TMR) method using Mg powder as the reactant. The PSSs obtained by MMR reaction has higher structural integrity than that fabricated by TMR. After encapsulation with reduced graphene oxide, the Si/C composite exhibits superior cycling stability and rates such as a high reversible capacity of 1034 mAh·g−1 at 0.5C (4200 mAh·g−1 at 1.0C) after 1000 cycles, capacity retention of 79.5%, and high rate capacity of 497 mAh·g−1 at 2.0C. This strategy offers a new route to fabricate high-performance porous Si anodes and can be extended to other materials such as germanium.