One-step synthesis of spherical Si/C composites with onion-like buffer structure as high-performance anodes for lithium-ion batteries

Silicon (Si) is the most promising next-generation anode of lithium-ion batteries (LIBs), which has attracted considerable interest due to its high theoretical capacity, low lithium storage potential and rich resource reserves. However, the development of Si anode is still hindered by many obstacles, such as large volume change during lithium insertion/extraction and low electrical conductivity. Recently, abundant Si/C composites have been designed to overcome the problems of Si anode. However, most preparation methods are complicated and difficult for industrialized applications and the Si nanoparticles in composites are usually coated with disorder carbon. In this work, we designed an onion-like Si/C composite through a simple one-step injection pyrolysis using pyridine as the carbon source. In this way, Si nanoparticles were successfully encapsulated into onion-like carbon shells. When used as the anode material for LIBs, this composite exhibits outstanding Li-storage performance with the capacity as high as 1391 mAh g−1 after 400 cycles at a current density of 0.2 A g−1 and rate capacity retention of 63.9% at 2 A g−1 to 200 mA g−1. The excellent electrochemical performance mainly benefits from higher structure stability and better buffer effect of the unique onion-like structure for expanded Si nanoparticles. In addition, in this process we can easily control the lithium storage capacity and particle size in gradient through changing the raw material ratio of pyridine to Si nanoparticles. Hence, we have developed a facile method to prepare onion-like Si/C anodes, which can effectively improve the capacity and cycle life of commercial LIBs.