Tuning density of Si nanoparticles on graphene sheets in graphene-Si aerogels for stable lithium ion batteries.

Silicon is one of the most promising candidates for anodes of lithium ion batteries attributed to the highest theoretical specific capacity (4200 mAh/g). However, the conductivity and structural integrity during the lithiation-delithiation process are very poor, which seriously affect the actual electrochemical performance. To address these issues, we introduce graphene framework as both structural skeletons and conductive networks for silicon in this work. Through a facile freeze-drying approach, Si nanoparticles are successfully anchored on graphene sheets uniformly, and graphene form strong and conductive framework, which serves as mechanical support, electrical network, and buffer layer for Si, highly improving the structural integrity and conductivity. The electrochemical examinations indicate that the synthesized graphene-Si aerogels can deliver 104% specific capacity retention after cycled for 195 times at 0.8 A/g. Multi-walled carbon nanotubes are utilized to improve the rate property, and the resulting anode exhibits average specific capacities of 1415, 1209, 1057, 888, 781, and 646 mAh/g at charge/discharge rates of 0.05 C, 0.18 C, 0.2 C, 0.5 C, 1 C, and 2 C, respectively. Benefit from the facile synthesis and excellent cycling stability, it is expected that graphene-Si aerogels may play an important role in lithium ion battery.